Much though I love the games, I had to vote for gen V having the worst starters.
Personally, I really dislike the gen II starters, but they're at least not bad. The gen V starters though - the only one that's really late-game viable is Samurott, and a lot of that is due to the shortage of other waters in the Unova dex. Emboar is okay, but it's not even as good as the past Fire/Fighting starters and has a lot of competition in this gen from other, and better, Fire types. And poor Serperior is outclassed almost immediately by either Lilligant or Leavanny, depending on your preferences. Coil helps a bit, but it's too little, too late.