Heh, looks like both of my favorites are some of the least liked by most.
It's a tough call between Gen 2 & 5's starters for me. All of Gen 5's starters are awesome, with Tepig being my favorite by a mile. But Gen 2 wins out between the two because I have a hard time choosing between a starter whenever I play a Johto game. It might be partially nostalgia talking, but I like all of the Johto crew equally.The first stages are all adorable, the middle stages are pretty cool (minus Croconaw, his proportions seem odd), and the final forms being just plain awesome!
So Gen 2 has the best starters for me, with Gen 5 coming in a close second.
Least favorite starter set is Gen 3's, with 4's getting an honorable mention.