Snivy's final form is Serperior.
Cons: He is has a shallow movepool, and low offenses
Pros: High Speed, High defenses, and an amazing ability that counteracts his low offenses and shallow movepool. Contrary! it reverses stat changes EI: Serperior uses Leaf-storm and his S.Attack gets boosted by 2 stages as opposed to being lowered by 2 stages.
He is definitely the strongest competitively, if you do not want to use a Sweeper set you can even go Sub-seeder or Wall of another kind, he can even be a Coil tank.
Oshowatt's final form is Samurott
Cons: rather small movepool, below average speed, below average defenses.
Pros: Good offenses and some strong moves
Samurott may be the weakest the three, he is too slow to sweep effectively without Choice scarf or Trick-room and is not bulky enough to be a tank. He can be useful in the lower tiers however.
Tepig's final fo.....*psst turn around...............
Tepig's final form is Emboar
Cons: Low defenses, Low speed, and being ugly
Pros: Pretty good movepool, High Attack, good Special attack, and High HP.
He can be great with T-room, and good with Choice-scarf, but unfortunately his defenses are too low to be a tank.