Here's how I see it:
The definitive starter for the Kanto games is Charmander. Maybe it's overrated, but it gives your adventure a lot more meaning. It's the only one that will face a challenge at the first gym, making a player realize that to become a true trainer, they must catch em all! Plus it means that Red chooses the red starter, and Blue chooses the blue starter (matchy :3)
So if you want the classic adventure, go Charmander. Of course, if you're just looking to beat the game as easily as possible, I guess Squirtle. While Bulbasaur will get you through the first 2 gyms and have a resistance to Lt. Surge, you'll begin to struggle as you face later gyms like Erika, Sabrina (psychic>poison), Koga, and Blaine.