In my personal Black 2 playthrough I can't give much real insight because I traded in four level ones (Mienfoo, Gollett, Axew, and Vanillite) after I beat Cheren, abandoned my starter immediately afterwards and only found one other permanent team member (N's Zorua) in the rest of the game. Though I think I can add some helpful information...
Golurk: - Low/Mid Tier (probably low)
Availability: Incredibly Late (Victory Road), around level 50.
Stats: Not bad, though it will be missing the missing the EVs your other team members have it can tank reasonably well and hit hard on the physical end, but will almost never hit first.
Typing: Ground/Ghost gives interesting immunities and fairly useful Stabs especially for the endgame, but the Ghost and Dark weaknesses will be problematic.
Movepool: It's downright bizarre. When you capture Golurk it will know Curse and learn Earthquake within two levels (unless it already has it). Rock Slide, Fly, Brick Break, and Shadow punch are other usable options before resorting to tutors. From Tutors the options include Elemental Punches, Drain Punch, Superpower, and Zen Headbutt but you probably have much better trained pokemon to use your shards on.
Major Battles: Hugh - if it's been leveled a little and has been taught the right attacks it can perform pretty well againts his Unfezant, Bouffalant, and maybe even Emboar.
Shauntal - If it knows Shadow Punch you can hit all of her pokemon pretty hard, but you don't want to take a hit and only her Cofagrigus and possibly Golurk will be slower than you.
Grimsley - No
Caitlin - Same deal as Shauntal, but Golurk does make a decent switch in if you need one.
Marshal - Throh will destroy Golurk and Sawk is risky as well, though if you have Fly Mienshao could be defeated very easily and Conkeldurr should not provide much resistance either. Still, you're probably best off using Golurk as an emergency switch in
Iris - Aggron should present no trouble at all, and a Golurk could feasibly Challenge Archeops, Druddigon, and if you're feeling lucky, Haxorus. But the best use for one is an emergency switch in.
Additional Comments: Golurk isn't that bad at all, it just comes very late when you have much better options or trained Pokemon and its performance in major battles is underwhelming. But if you have a spare slot in your team, a member with horrendous endgame, or member that has no use outside of being an HM slave Golurk certainly should be considered. Golurk also pairs very well with Zoroark, just because of Illusion and their typings.
Zorua: - High/Top Tier (the odd playstyle to use it probably means high)
Availability: You get one for free in Driftviel (Midgame)
Stats: It's pretty frail, but that speed and special attack are just great. Physical attack, while overlooked, is no slouch either so it's very easy and effective to go mixed.
Typing: Dark Type is very good endgame, between STAB and psychic immunity it's quite useful. Mid game coverage is also quite good, even though it's mostly neutral. Just watch out for Fighting types.
Movepool: Small but precise. Teach it Snarl, Zoroark's special attack makes up for the low base power and the special attack drops are very helpful to teammates. Foul Play, Night Daze, Dig, U-Turn, Flamethrower, and possibly a boosting move are just about the only other moves worth using, but you rarely need more with Zoroark.
Major Battles: Zoroark is an interesting case, other than Skylla's Swoobat, Marlon's Jellicent, Colress's Beheeyem, Ghetsis's Cofagrigus, Shauntal, and Caitlin Zoroark isn't an obvious choice, but through smart use of Illusion a Zoroark can easily win battles where it would be expected to struggle. U-turn, special attack drops from snarl, and Psychic Immunity only add to the utility illusion gives. It should be noted that Zoroark is not a sweeper, and should usually U-turn out once Illusion is broken (but that can take longer than one might might expect depending on how Illusion is used).
It's fairly easy to beat the Pokemon League (other than Iris) using only a Zoroark and a Fighting Type.
Additional Comments: Being owned originally by N, Zorua will gain experience much more quickly than other pokemon, further adding to its usefullness. And I can't express just how essential Illusion abuse is to using a Zoroark. You'll definitely want a fighting type when using a Zoroark (But fighting types are so useful, you have one anyway) and ghost types generally work well for illusion.
I'd like to see somebody review Mienfoo, I can't really give a good evaluation but it has an amazing endgame. Axew is also one to look into, it's found in Mistralton cave and Is pretty good throughout the game.
Golurk: - Low/Mid Tier (probably low)
Availability: Incredibly Late (Victory Road), around level 50.
Stats: Not bad, though it will be missing the missing the EVs your other team members have it can tank reasonably well and hit hard on the physical end, but will almost never hit first.
Typing: Ground/Ghost gives interesting immunities and fairly useful Stabs especially for the endgame, but the Ghost and Dark weaknesses will be problematic.
Movepool: It's downright bizarre. When you capture Golurk it will know Curse and learn Earthquake within two levels (unless it already has it). Rock Slide, Fly, Brick Break, and Shadow punch are other usable options before resorting to tutors. From Tutors the options include Elemental Punches, Drain Punch, Superpower, and Zen Headbutt but you probably have much better trained pokemon to use your shards on.
Major Battles: Hugh - if it's been leveled a little and has been taught the right attacks it can perform pretty well againts his Unfezant, Bouffalant, and maybe even Emboar.
Shauntal - If it knows Shadow Punch you can hit all of her pokemon pretty hard, but you don't want to take a hit and only her Cofagrigus and possibly Golurk will be slower than you.
Grimsley - No
Caitlin - Same deal as Shauntal, but Golurk does make a decent switch in if you need one.
Marshal - Throh will destroy Golurk and Sawk is risky as well, though if you have Fly Mienshao could be defeated very easily and Conkeldurr should not provide much resistance either. Still, you're probably best off using Golurk as an emergency switch in
Iris - Aggron should present no trouble at all, and a Golurk could feasibly Challenge Archeops, Druddigon, and if you're feeling lucky, Haxorus. But the best use for one is an emergency switch in.
Additional Comments: Golurk isn't that bad at all, it just comes very late when you have much better options or trained Pokemon and its performance in major battles is underwhelming. But if you have a spare slot in your team, a member with horrendous endgame, or member that has no use outside of being an HM slave Golurk certainly should be considered. Golurk also pairs very well with Zoroark, just because of Illusion and their typings.
Zorua: - High/Top Tier (the odd playstyle to use it probably means high)
Availability: You get one for free in Driftviel (Midgame)
Stats: It's pretty frail, but that speed and special attack are just great. Physical attack, while overlooked, is no slouch either so it's very easy and effective to go mixed.
Typing: Dark Type is very good endgame, between STAB and psychic immunity it's quite useful. Mid game coverage is also quite good, even though it's mostly neutral. Just watch out for Fighting types.
Movepool: Small but precise. Teach it Snarl, Zoroark's special attack makes up for the low base power and the special attack drops are very helpful to teammates. Foul Play, Night Daze, Dig, U-Turn, Flamethrower, and possibly a boosting move are just about the only other moves worth using, but you rarely need more with Zoroark.
Major Battles: Zoroark is an interesting case, other than Skylla's Swoobat, Marlon's Jellicent, Colress's Beheeyem, Ghetsis's Cofagrigus, Shauntal, and Caitlin Zoroark isn't an obvious choice, but through smart use of Illusion a Zoroark can easily win battles where it would be expected to struggle. U-turn, special attack drops from snarl, and Psychic Immunity only add to the utility illusion gives. It should be noted that Zoroark is not a sweeper, and should usually U-turn out once Illusion is broken (but that can take longer than one might might expect depending on how Illusion is used).
It's fairly easy to beat the Pokemon League (other than Iris) using only a Zoroark and a Fighting Type.
Additional Comments: Being owned originally by N, Zorua will gain experience much more quickly than other pokemon, further adding to its usefullness. And I can't express just how essential Illusion abuse is to using a Zoroark. You'll definitely want a fighting type when using a Zoroark (But fighting types are so useful, you have one anyway) and ghost types generally work well for illusion.
I'd like to see somebody review Mienfoo, I can't really give a good evaluation but it has an amazing endgame. Axew is also one to look into, it's found in Mistralton cave and Is pretty good throughout the game.