I wouldn't particularly recommend pyro for a beginner at the minute, hes very dependant on his unlocks, especially the degreaser and axtinguisher. I've got a spare axtinguisher if you are interested in pyro.
Heavy is a pretty good class out the box, though he can be a little frustrating on some of the bigger maps due to his slow speed. The G.R.U really helps with this once you've got one.
Medic is a fairly decent class to play since he can observe other players quite a bit more than the other classes since the medic gun locks onto the target.
spy might be a little difficult for a new player, as might sniper, though if you've played any other fps before sniper probably wouldn't be too bad. Though do note that most people don't like too many snipers and spies on a team, especially on the attacking team, so please try to keep that on mind. Though if one of them do become your favorite class don't worry about it too much and just have fun.
I've got a few spare unlocks if you don't have many, feel free to add me on steam and send a message to me the next time the 2 of us are online, I'll be happy to give you some. Though I'd recommend sticking to some of the default weapons for most classes till you have a better idea about how the classes work, though some weapons are pretty much instant upgrades that you'll probably want as soon as possible. The degreaser and axtinguisher for pyro, a new medic melee, equaliser for soldier and the G.R.U for heavy are probably the best examples right now.
Hope this helps and welcome to the game