Well, this is my discovery, I think everyone has already known.
Each Pokemon game has a, hmm, particular pattern in starters. But this time in Black 2/White 2, it's a little bit different, and rather balanced than other games.
If you want to be a strong physical attacker, then Tepig will be you choice, cuz' Emboar is really strong with different physical moves available for it.
If you like not to contact with your opponent, that means you like special attacks, then Oshawott is great. Some strong special attacks can be even awesome if you give it to Samurott.
And finally, this is a little bit special. If you're neither a physical attacker nor a special attacker, and you wanna be balanced, Snivy will be your choice. Because learnable physical attack moves and special attack moves for it are similar, and so for Serperior.
The above stuffs are from my study of the three starters and previous generation games.
Emboar has the highest attack stat among the three when you EV train it's attack stat specifically. Maximum can be 379;
Samurott has the highest sp. attack stat, which is 346 in max;
Serperior has the same max value of attack and sp. attack, both are 273. Additionally it's the fastest among the three if you get the max speed stat of it.
Okay here are my own opinion: I'm a physical attacker, so I'll choose Tepig. There are less useful moves that can be learnt by Serperior; Samurott is great too, but I'll try that if I restart the game. Well, actually I won't have to choose a starter, because the three starters are the first three Pokemon I'll have in each Pokemon games. The three starters of each game will always be my favourite besides legendary Pokemon of that title. So... why can't I have all three? What's the meaning of playing games if you can't own what you want in the games, specially when you're able to get it. Well, those are just my own opinion. Please don't bomb me if you dislike it...=P