(NOTE: This only applies to Red/Blue/Green. I have not played the future games, so you'll have to educate me on how things are in them, as I am an idiot.)

I do not like Fire Pokémon. I never really have one on my team, and I've figured out specifically WHY.

And it's not just because picking Charmander at the beginning of the game makes the game itself slightly tougher, no. That's a pointless argument, because I ALWAYS pick Squirtle. ALWAYS.

The problem with Fire-type Pokémon is this:

While they do have a slightly higher attack stat than most other Pokémon it seems, there's just not a large number of Fire-types, at least in Red and Blue/Green. There may be more of them in the later games, but I know next to nothing about them and therefore am not an expert with those.
But seriously, in Fire Red, if you do not pick Charmander, like I didn't, and you want a Fire-type Pokémon, there's not a lot to choose from. There's Growlithe, Ponyta, and Moltres. And Flareon, should you choose to give your Eevee the Fire Stone (I didn't). That's four, count'em, FOUR Pokémon to choose from, not including the evolutions of Growlithe and Ponyta, since Arcanine requires a Fire Stone and I can't remember whether or not you can actually catch a Rapidash. If you have Blue/Leaf Green, Growlithe/Arcanine is replaced by Vulpix/Ninetales, and you have one extra choice, the immensely goofy-looking (but admittedly loveable) Magmar. So, including Charmander and everyone's evolutions, that gives you a whopping...ELEVEN fire-types. Eleven out of one hundred and fifty Pokémon. Laym.

Compare that the much larger number of Water and Grass-type Pokémon. No, I'm not going to count those, you can do that yourselves. Our firey friends are quite outnumbered.

And even if you do have one or two Fire-types on your team, that doesn't necessarily put you at a huge advantage...unless you have Moltres, but having ANY Legendary bird will put you at a nice advantage, and the same goes for Charizard if you did pick Charmander in the beginning.
Fire is only Super Effective against three other types: Bug, Grass, and Ice. Now granted, no single element dominates over all other elements, but of the three that Fire can destroy, it's kind of screwed.

For one thing, with only a few exceptions, none of the higher-level trainers actually use Bug-type Pokémon. They're like a novelty for kids. Once you pass about halfway through the game, the number of Bug Catchers just drops significantly you hardly trouble yourself with insects ever again, aside from the few exceptions. And, you know, while fighting a Weedle or Caterpie is like bullying a small child, fighting Kakuna and Metapod is like fighting a paraplegic with downs syndrome, there's nothing to brag about there, and I don't care what level it's at.

Now there ARE a lot of Grass-type Pokémon, but they are by no means helpless. Most of them, in fact, are dual-type, the majority of those paired up with Poison. And any seasoned trainer can tell you how quickly the Poison status ailment can seriously fuck you up. You also run across some Grass/Ground-types, like Venusaur. And hey look, Ground attacks are Super Effective against Fire! Unless, once again, you're using Moltres. And while I mentioned Poison, let us not forget the other status ailments that any good Grass-type loves to hit you with: Sleep and Paralysis! You're screwed if your Fire-type is slower than it's opponent, I'm afraid.

But wait, I hear some of you cry, what about the status ailment Burn? Well, we've already established that there aren't very many Fire-type Pokémon, so you're not at great risk. Honestly, I can count on one hand the number of times one of my Pokémon has burned, or been burned by, an enemy. I played a LOT of Pokémon as a kid, so out of possibly thousands of battles, a few occurances of a burn is pretty meek.

And Ice-types, well, there's a PRETTY GOOD chance that they also know at least one Water attack. And we all know what happens when water and fire meet, right kids? Exactly.

So there you have it: Fire-type Pokémon pretty much suck. Feel free to educate me if things are drastically different in the future titles, as I once owned Silver, but don't remember a single thing about it, and never really bothered after that...

-Brett