No doubt, the best class in the game.
Very easy to pick up, can counter almost everyone if they make mistakes.
The only mistake you can make when fighting a pyro is being predictable.
Cuz if you are predictable, he will:
Flare crit you,
Airblast your projectiles back to you,
Deal more high-risk high-reward damage (shotgun flicks, or "flame flicks"; basically you walk into his flames)
then again there are some weapons that are unbalanced and are very easy to use
examples include:
The Backburner (why do you get random crits from the front as well?)
The Scorch Shot (legit aim anywhere and there is a 50% chance you will ignite someone)
The Back Scratcher (a direct upgrade from stock, because you get more health from health packs and you help your medic build faster)