I personally like Snivy better; because its art design makes it look very calm and collected, and according to the pokedex in Pokemon Black, its pretty smart too! So yeah, I'm a fan of its personality. :3 And also, I LOVE its Contrary ability from Dream World; the one where moves that lower stats are instead raised? So say, if one used Leaf Storm, instead of the -2 Special attack drop, the ability raises its special attack by 2! So, I found Snivy more useful than Treeko, IMO~