Edit: Changes in Bold print
Well, I've been playing ADV for a long time now, and this is the team I've ended up with. I like this team, and it does very well on Netbattle, though it still has some issues at times, so I thought I'd get some opinions on it and hopefully be able to improve this team even more.
Gengar (M) @ Leftovers
Trait: Levitate
EVs: 40 Atk / 252 Spd / 216 SAtk
Naive Nature (+Spd, -Sp.Def)
- Destiny Bond
- Focus Punch
- Ice Punch
- Thunderbolt
Pretty standard Gengar, and serve's as my lead. Thunderbolt for Gyarados, Ice punch for Salamence... and it's like a mini-boltbeam anyways. Hypnosis to put anything I can't handle to sleep, and Destiny bond to try and bring down a pokemon I have trouble with, or just to get Gengar one last KO before it goes down. I prefer timid Gengar to outspeed as much as possible... and like this I outspeed adamant Swellow by 1 point lol.
Quagsire (M) @ Leftovers
Trait: Water Absorb
EVs: 148 HP / 252 Atk / 40 Def / 68 SDef
Adamant Nature (+Atk, -SAtk)
- Hidden Power Rock
- Focus Punch
- Earthquake
- Yawn
Ah, how I love Quagsire. I use him mainly to force switches with yawn, then hit the next pokemon that comes out with a nice Focus Punch to the face. Safeguard is there to protect my team from status (Mainly Blaziken), and Hidden Power Rock is so fliers don't totally wall me. Note: I specifically use Quagsire over Swampert because of Water absorb, safeguard, and yawnpunching, all of which Swampert is unable to do, so please don't suggest him, as I used him at one point, and Quagsire just does much better than him, for me at least. Max attack to maximize output, and major special defense investment to keep his defenses nice on both ends, making him somewhat difficult to KO. Though, if anyone has suggestions on adjusting Quagsire's EVs to make it even sturdier on both ends, please, give me your suggestion. Though I find with this he doesn't take much from Ice Beam, and CB Rock Slide coming from Aerodactyl isn't a huge issue either.
Skarmory (M) @ Leftovers
Trait: Sturdy
EVs: 252 HP / 56 Atk / 192 Def / 8 Spd
Impish Nature (+Def, -SAtk)
- Roar
- Spikes
- Drill Peck
- Taunt
My physical wall. Spikes is there for obvious reasons (Also makes Quagsire's subpunching so much more valuable), as Roar is also an obvious choice. Substitute is usually my first act, to test the waters and see what they bring in on Skarmory (Namely Magneton lure), and then roar them out, knowing what they use to deal with Skarm. Taunt is to prevent other Skarmory, or even Forretress to use spikes whilst I do, as otherwise we'd just be using spikes for 3 turns in a row... The 8 speed EVs is to outrun other Skarmory, so I can: a) Taunt them before they can use spikes, or even rest, and b) So I can roar them out before they roar me out.
Blissey (F) @ Leftovers
Trait: Natural Cure
EVs: 100 HP / 252 Def / 156 SDef
Bold Nature (+Def, -Atk)
- Aromatherapy
- Counter
- Softboiled
- Thunder Wave
Yeah, I use Skarmory and Blissey, so sue me. They are still not an unbeatable combination (Magmar, Electabuzz, Blaziken deal with them fine). Well, this is essentially the cleric set, but I opted Seismic Toss/Ice Beam out for counter. Trust me, when Aerodactyl's and Dugtrio switch in to try and 2HKO me, its very handy. Sure, I can't do anything to special attackers, but they can't do anything to me either :)
Blaziken (F) @ Salac Berry
Trait: Blaze
EVs: 76 HP / 252 Atk / 180 Spd
Hasty Nature (+Spd, -Def)
- Endure
- Hidden Power [Ice]
- Fire Blast
- Reversal
Reversal Blaziken. You know the deal, Endure an incoming Earthquake, Surf, or Psychic for the salac boost and sweep away with Reversal. Overheat is for Skarmory/Forretress/Weezing, and Hidden Power Ice for Salamence. I almost always save Blaziken for late-game, and by that time, most of their team should be worn down to fairly low HP, allowing me to get away with the sweep, and meaning I don't really need to have Swords Dance, as everything should be within KO range, so I opted for more coverage.
Gardevoir (F) @ Leftovers
Trait: Trace
EVs: 252 HP / 76 Def / 180 Spd
Modest Nature (+SAtk, -Atk)
- Calm Mind
- Fire Punch
- Psychic
- Wish
And Gardevoir is my valued 6th member. A great calm mind pokemon, taking little from special hits after 1 or 2 boosts, and being able to cripple physical attackers with Will-O-Wisp. Psychic for STAB, and Fire punch for steels. I especially chose Fire Punch for Magneton, as if I manage to find a magneton on their team when I sub with Skarmory, then I can predict their switch next turn, and switch to Gardevoir, as she traces Magnet pull, trapping Magneton. Then I can just calm mind (As generally I don't take much damage from it) and KO with Fire punch. Trace also works great against Vaporeon/Jolteon, neither of which can do much to me after tracing Water/Volt absorb. The speed is to outrun Adamant Breloom, but I realize, it ties with Jolly Tyranitar... should I sacrifice a slight bit of defense to raise my speed some more? I didn't see the need, as I can just switch out, but... perhaps I'm being too cocky.
And that is my team. I love it, because I got to use all my favorite's (Gardevoir, Blaziken, Quagsire, Gengar, and Skarmory lol) and it's efficient. Long, I know, but I like to go in-depth, so you have more info to judge my team with and offer suggestions. Though, I do have issues with Taunt Gyarados and Taunt Tyranitar (As only Gengar can do some damage to Gyarados, and seeing as my Blaziken is a reversal set, it won't handle Tyranitar, due to sandstorm... but at least Tyranitar takes Spikes damage, Gyarados is immune to it :( ). Though, sometimes I get lucky and counter them to death with Blissey, it's a risky manouever, and I have no surefire ways to deal with them. And yes, I am primarily a defensive player, as I dislike playing offensively quite a bit...
Well, I've been playing ADV for a long time now, and this is the team I've ended up with. I like this team, and it does very well on Netbattle, though it still has some issues at times, so I thought I'd get some opinions on it and hopefully be able to improve this team even more.

Gengar (M) @ Leftovers
Trait: Levitate
EVs: 40 Atk / 252 Spd / 216 SAtk
Naive Nature (+Spd, -Sp.Def)
- Destiny Bond
- Focus Punch
- Ice Punch
- Thunderbolt
Pretty standard Gengar, and serve's as my lead. Thunderbolt for Gyarados, Ice punch for Salamence... and it's like a mini-boltbeam anyways. Hypnosis to put anything I can't handle to sleep, and Destiny bond to try and bring down a pokemon I have trouble with, or just to get Gengar one last KO before it goes down. I prefer timid Gengar to outspeed as much as possible... and like this I outspeed adamant Swellow by 1 point lol.

Quagsire (M) @ Leftovers
Trait: Water Absorb
EVs: 148 HP / 252 Atk / 40 Def / 68 SDef
Adamant Nature (+Atk, -SAtk)
- Hidden Power Rock
- Focus Punch
- Earthquake
- Yawn
Ah, how I love Quagsire. I use him mainly to force switches with yawn, then hit the next pokemon that comes out with a nice Focus Punch to the face. Safeguard is there to protect my team from status (Mainly Blaziken), and Hidden Power Rock is so fliers don't totally wall me. Note: I specifically use Quagsire over Swampert because of Water absorb, safeguard, and yawnpunching, all of which Swampert is unable to do, so please don't suggest him, as I used him at one point, and Quagsire just does much better than him, for me at least. Max attack to maximize output, and major special defense investment to keep his defenses nice on both ends, making him somewhat difficult to KO. Though, if anyone has suggestions on adjusting Quagsire's EVs to make it even sturdier on both ends, please, give me your suggestion. Though I find with this he doesn't take much from Ice Beam, and CB Rock Slide coming from Aerodactyl isn't a huge issue either.

Skarmory (M) @ Leftovers
Trait: Sturdy
EVs: 252 HP / 56 Atk / 192 Def / 8 Spd
Impish Nature (+Def, -SAtk)
- Roar
- Spikes
- Drill Peck
- Taunt
My physical wall. Spikes is there for obvious reasons (Also makes Quagsire's subpunching so much more valuable), as Roar is also an obvious choice. Substitute is usually my first act, to test the waters and see what they bring in on Skarmory (Namely Magneton lure), and then roar them out, knowing what they use to deal with Skarm. Taunt is to prevent other Skarmory, or even Forretress to use spikes whilst I do, as otherwise we'd just be using spikes for 3 turns in a row... The 8 speed EVs is to outrun other Skarmory, so I can: a) Taunt them before they can use spikes, or even rest, and b) So I can roar them out before they roar me out.

Blissey (F) @ Leftovers
Trait: Natural Cure
EVs: 100 HP / 252 Def / 156 SDef
Bold Nature (+Def, -Atk)
- Aromatherapy
- Counter
- Softboiled
- Thunder Wave
Yeah, I use Skarmory and Blissey, so sue me. They are still not an unbeatable combination (Magmar, Electabuzz, Blaziken deal with them fine). Well, this is essentially the cleric set, but I opted Seismic Toss/Ice Beam out for counter. Trust me, when Aerodactyl's and Dugtrio switch in to try and 2HKO me, its very handy. Sure, I can't do anything to special attackers, but they can't do anything to me either :)

Blaziken (F) @ Salac Berry
Trait: Blaze
EVs: 76 HP / 252 Atk / 180 Spd
Hasty Nature (+Spd, -Def)
- Endure
- Hidden Power [Ice]
- Fire Blast
- Reversal
Reversal Blaziken. You know the deal, Endure an incoming Earthquake, Surf, or Psychic for the salac boost and sweep away with Reversal. Overheat is for Skarmory/Forretress/Weezing, and Hidden Power Ice for Salamence. I almost always save Blaziken for late-game, and by that time, most of their team should be worn down to fairly low HP, allowing me to get away with the sweep, and meaning I don't really need to have Swords Dance, as everything should be within KO range, so I opted for more coverage.

Gardevoir (F) @ Leftovers
Trait: Trace
EVs: 252 HP / 76 Def / 180 Spd
Modest Nature (+SAtk, -Atk)
- Calm Mind
- Fire Punch
- Psychic
- Wish
And Gardevoir is my valued 6th member. A great calm mind pokemon, taking little from special hits after 1 or 2 boosts, and being able to cripple physical attackers with Will-O-Wisp. Psychic for STAB, and Fire punch for steels. I especially chose Fire Punch for Magneton, as if I manage to find a magneton on their team when I sub with Skarmory, then I can predict their switch next turn, and switch to Gardevoir, as she traces Magnet pull, trapping Magneton. Then I can just calm mind (As generally I don't take much damage from it) and KO with Fire punch. Trace also works great against Vaporeon/Jolteon, neither of which can do much to me after tracing Water/Volt absorb. The speed is to outrun Adamant Breloom, but I realize, it ties with Jolly Tyranitar... should I sacrifice a slight bit of defense to raise my speed some more? I didn't see the need, as I can just switch out, but... perhaps I'm being too cocky.
And that is my team. I love it, because I got to use all my favorite's (Gardevoir, Blaziken, Quagsire, Gengar, and Skarmory lol) and it's efficient. Long, I know, but I like to go in-depth, so you have more info to judge my team with and offer suggestions. Though, I do have issues with Taunt Gyarados and Taunt Tyranitar (As only Gengar can do some damage to Gyarados, and seeing as my Blaziken is a reversal set, it won't handle Tyranitar, due to sandstorm... but at least Tyranitar takes Spikes damage, Gyarados is immune to it :( ). Though, sometimes I get lucky and counter them to death with Blissey, it's a risky manouever, and I have no surefire ways to deal with them. And yes, I am primarily a defensive player, as I dislike playing offensively quite a bit...