On the contrary, Charizard is actually the most challenging choice for starter. In the first generation, Charmander was horrible for the first two gyms. At least in FireRed and LeafGreen, Charmander learns Metal Claw just for the Pewter gym and Mount Moon. Still, battling Misty is total heck unless you caught a grass type such as a Paras in Mount Moon or a Oddish or Bellsprout in the field next to Nugget Bridge.
My favorite starters are Torchic and Mudkip, so it is a hard decision when trying to select only one. I tend to choose Torchic for its very awesome Fire/Fighting typing (well, not like that's anything special after Infernape and that pig Emboar). FireRed I like Bulbasaur, though I've played through with Charizard in the past and used to choose Squirtle in the originals.