Bulbasaur is strong in any capacity, containing high physical power, for Tackle and Strength, and magical attack, like Razor Leaf and Solarbeam. Along with those offensively intimidating abilities, the Bulbasaur line is the proud owner of Sleep Powder and Leech Seed. (Leech Seed, back in the day, was an obscure skill, not unlike how Leaf Blade was rare in Ruby/Sapphire/Emerald.)
Charmander is respectfully tough to level, equally tough to hate as well. Despite being a Fire/Flying type, Charizard has quite an assortment of non-Fire/Flying moves, such as Metal Claw, Slash and Dragon Rage. FR/LF have an advantage over its retro counterparts in the manner that Charizard can now learn and use Fly! (Thanks for noticing, GameFreak.) Even w/out Fly, the Charmander line learns Flamethrower and Wing Attack, suitable for the final form.
Squirtle is not weak in any circumstances, despite being the only singular-typed starter throughout the entire line. Just like how Charizard can learn Fly, the Blastoise line, even Squirtle itself can learn Surf. (Yaay!!) Skull Bash doesn't suck, provided you don't mind the 'wasted' turn. (I hate Skull Bash with a passion, but even I will use it, given the proper opportunity.) Bite is an awesome Dark move. (Again, thanks, GameFreak for converting Bite's move-type.) And bless 'em for giving the Squirtle line access to Rain Dance.
All of the above pokemon are compelling and are recommended for use by me, your friendly neighbourhood Pokemon enthusiast.
Woow look like Charmader is too popular here.