Last Draggy discussion was in early February and wasn't well laid out.
Dragonite (Dragon / Flying)
Base Stats: 91 HP / 134 Atk / 95 Def / 100 SAtk / 100 SDef / 80 Spd
Ability: Inner Focus (Prevents flinching)
Since Salamence and Dragonite are pretty much competing for the DD dragon or special dragon position I'll bold those things that Dragonite has over Salamence. Italics will be what Dragonite has over the physical Garchomp.
Notable Physical Movepool
Dragon Claw
Dragon Dive
Outrage
Fire Punch
Thunderpunch
Ice Punch
Aqua Tail
Waterfall
Focus Punch
Brick Beak
Aerial Ace
Stone Edge
Rock Slide
Earthquake
Notable Special Movepool
Dragon Pulse
Meteoric Swarm
Ice Beam
Blizzard
Thunderbolt
Thunder
Flamethrower
Fire Blast
Focus Bomb
Surf
Notable Support Moves
Thunder Wave
Dragon Dance
Feather Rest
Substitute
Light Screen
Haze
Heal Bell (XD)
When looking at Dragonite's movepool in that way you can see that there's plenty of things that Draggy can do that Salamence and Garchomp can't. There's one major reason, though, that Garchomp and Salamence are usually preferred over Dragonite: their base stat allocations. Dragonite has a measly 80 speed as compared to Salamence's 100 and Garchomp's 102. Its SAtk is 100 compared to Salamence's 110. Despite this, Dragonite's vastly superior movepool makes it a good choice over Salamence and Garchomp IMO if your team needs a varied sweeper.
Dragonite @ Leftovers
Nature: Modest (+SAtk -Atk)
Trait: Inner Focus
EVs: 200 HP / 104 Def / 148 SAtk / 56 SDef
-Thunderbolt
-Ice Beam / Dragon Pulse
-Focus Bomb
-Feather Rest
Hits everything in the game not named Shedinja for at least neutral damage. Thunderbolt will usually OHKO Jumpman's bulky Gyarados, but Phuquoph's has a better chance of surviving thanks to those special defense EVs. Ice Fang from Gyarados is always a 2HKO against Dragonite before +2 DD, meaning Draggy can't switch into it but can threaten Gyarados should it get in. Ice Beam is better than Dragon Pulse at taking on any dragon not named Kingdra, but Dragon Pulse deals more damage to other opponents. Focus Bomb hits TTar hard and does reasonable damage to Blissey (should it hit).
Dragonite @ Choice Glasses
Nature: Timid (+Spd -Atk) or Modest (+SAtk -Atk)
Trait: Inner Focus
EVs: 4 HP / 252 SAtk / 252 Spd
-Thunderbolt
-Ice Beam
-Dragon Pulse / Meteoric Swarm
-Focus Bomb
Salamence is probably better at this, but it's worth mentioning because Draggy has boltbeam.
Dragonite @ Leftovers
Nature: Adamant (+Atk -SAtk)
Trait: Inner Focus
EVs: 40 HP / 252 Atk / 216 Spd
-Dragon Dance
-Outrage
-Fire Blast
-Earthquake
DD Outrage kills a LOT of stuff. Fire Blast is for Skarmory and Bronzong, Earthquake is for Metagross / Jirachi / etc.
Dragonite (Dragon / Flying)
Base Stats: 91 HP / 134 Atk / 95 Def / 100 SAtk / 100 SDef / 80 Spd
Ability: Inner Focus (Prevents flinching)
Since Salamence and Dragonite are pretty much competing for the DD dragon or special dragon position I'll bold those things that Dragonite has over Salamence. Italics will be what Dragonite has over the physical Garchomp.
Notable Physical Movepool
Dragon Claw
Dragon Dive
Outrage
Fire Punch
Thunderpunch
Ice Punch
Aqua Tail
Waterfall
Focus Punch
Brick Beak
Aerial Ace
Stone Edge
Rock Slide
Earthquake
Notable Special Movepool
Dragon Pulse
Meteoric Swarm
Ice Beam
Blizzard
Thunderbolt
Thunder
Flamethrower
Fire Blast
Focus Bomb
Surf
Notable Support Moves
Thunder Wave
Dragon Dance
Feather Rest
Substitute
Light Screen
Haze
Heal Bell (XD)
When looking at Dragonite's movepool in that way you can see that there's plenty of things that Draggy can do that Salamence and Garchomp can't. There's one major reason, though, that Garchomp and Salamence are usually preferred over Dragonite: their base stat allocations. Dragonite has a measly 80 speed as compared to Salamence's 100 and Garchomp's 102. Its SAtk is 100 compared to Salamence's 110. Despite this, Dragonite's vastly superior movepool makes it a good choice over Salamence and Garchomp IMO if your team needs a varied sweeper.
Dragonite @ Leftovers
Nature: Modest (+SAtk -Atk)
Trait: Inner Focus
EVs: 200 HP / 104 Def / 148 SAtk / 56 SDef
-Thunderbolt
-Ice Beam / Dragon Pulse
-Focus Bomb
-Feather Rest
Hits everything in the game not named Shedinja for at least neutral damage. Thunderbolt will usually OHKO Jumpman's bulky Gyarados, but Phuquoph's has a better chance of surviving thanks to those special defense EVs. Ice Fang from Gyarados is always a 2HKO against Dragonite before +2 DD, meaning Draggy can't switch into it but can threaten Gyarados should it get in. Ice Beam is better than Dragon Pulse at taking on any dragon not named Kingdra, but Dragon Pulse deals more damage to other opponents. Focus Bomb hits TTar hard and does reasonable damage to Blissey (should it hit).
Dragonite @ Choice Glasses
Nature: Timid (+Spd -Atk) or Modest (+SAtk -Atk)
Trait: Inner Focus
EVs: 4 HP / 252 SAtk / 252 Spd
-Thunderbolt
-Ice Beam
-Dragon Pulse / Meteoric Swarm
-Focus Bomb
Salamence is probably better at this, but it's worth mentioning because Draggy has boltbeam.
Dragonite @ Leftovers
Nature: Adamant (+Atk -SAtk)
Trait: Inner Focus
EVs: 40 HP / 252 Atk / 216 Spd
-Dragon Dance
-Outrage
-Fire Blast
-Earthquake
DD Outrage kills a LOT of stuff. Fire Blast is for Skarmory and Bronzong, Earthquake is for Metagross / Jirachi / etc.