Gen V had bad starters. I researched which one I should pick, and ended up taking Snivy, turned out to be a bad decision, restarted and chose Oshawatt, still not that great. Restarted again, and picked Tepig. Still really bad, but I was tired of restarting. My final team in White was this:
I think that Gen I, Gen II, and Gen III had the best. Charmander, Squirtle, and Bulbasaur were awesome. Cyndaquil, Totodile (Especially Totodile), and Chikorita were decent. Torchic, Mudkip, and Treeko were really awesome (My personal favorites). Gen IV starters were good, just not good enough, Torterra, Infernape, and Empoleon looked amazing, but were just too susceptible to type disadvantages early in the game. Later on they were really good to have.
All that's just personal preference, though.