using Bulbasaur is basically easy mode; he tears through the first 2 gyms and resists the 3rd and 4th
Chikorita is unfortunately the absolute worst and is basically hard mode; being a slow "defensive" Grass type and getting completely bodied by the first 2 gyms just doesn't help at all. It's pretty rough, but it's a good challenge.
Treeko is the fastest; he's actually the only super-speedy Grass starter
Turtwig shows off the physical/special split by having high Attack and Defense, which would be considerably less usable before gen 4. That being said, he's still the hardest one to use. But hey, Earthquake through level up is awesome.
Snivy is... weird. It has high speed and defenses, and Grass isn't exactly the best defensive type. Plus, its best move through level up is Leaf Tornado for quite a while, so it is, yet again, the hard mode of the starters.
Chespin... I actually haven't played X/Y. I have no idea.
Rowlet is probably the strangest one. He trades his secondary Flying type for a Ghost type, and his stats are suited to mixed attacking and some "bulk" (Special Defense over physical defense) but his Attack is slightly higher than his Special Attack, and his physical attacks are way better anyway. Definitely the most interesting one.
