Since we started taking over the "Is Valve dropping hints?" thread, I figured this was worth posting.
The available unlocks so far are:
Medic: Blutsauger, Kritzkrieg, Ubersaw
Pyro: Flaregun, Backburner, Axestinguisher
Heavy: Sandvich, Natascha, K.G.B.
My setup and why: Medic: Blutsauger, Ubercharge, Ubersaw
The Blut is one of the most annoying guns in the game... First of all, the Medic is faster than every class than the Scout. Couple this with running backwards and firing these vampiric syringes and you can take out just about every class in one clip. Also I believe they're still bugged to crit (they're not supposed to crit, right?) Amazing gun.
I use Ubercharge because I just don't trust the person I'm healing the majority of the time (or they get blown up and I'm again stuck with someone I don't trust) and Ubercharge means at least I am going to live. Not so for the Kritzkrieg. Also Ubercharge vs Kritzkrieg... Uber wins unless you happen to find the one person who can't aim to save anyone's life and the Uber runs out.
Ubersaw because frankly that is probably the coolest looking melee weapon in the game, and you get Ubercharge for hitting people with it! It seems like it has amazing reach when you're on the receiving end. Also dual/triple medic chains are just hilarious (and they work) so deal with it :P
Pyro: Backburner, Shotgun, Axestinguisher
I use the Backburner because I actually sneak up on people a fair amount (whether or not it registers correctly is another issue...) and plan my attacks so that I'll come up behind at least 1 person. Also I just like the simplicity of left-click and for the life of me I can't figure out when to properly fire crap back at people and I actually forget I can do that half of the time with the regular gun equipped. However, I think that if you can master the compression blast you will be a much better Pyro/Player for it (so kudos to Pyros who are on their way to mastering it!)
I choose the Shotgun over the Flare Gun because most of the time it just makes more sense to me. If I find a need to put away my Backburner it's usually because I'm in the water (and I think hopping is lame) so pulling out a Flare Gun isn't going to do me much good. I prefer the feel of a Shotgun overall (it's probably my favorite weapon across all
FPS to begin with, though I prefer the FEAR iteration that blows people apart.) and unless you want to humiliate someone with 10hp by Flaring them to death, I don't find it all that useful (unless you're going to sneak up and chop them w/ the axe shortly afterwards...)
The Axestinguisher is just great. You can take down anything that's on fire in 1 hit the majority of the time (not always against Heavies.) There's no reason to use the Fire Axe unless you haven't unlocked the Axestinguisher yet or you don't bother setting people on fire first. (That's what "q" is for! Quickswitch ftw people)
Heavy: Sasha, Shotgun, K.G.B.
Sasha because Natascha is garbage. I only really see it being useful for slowing down a LARGE group of people for a demo to blow them up or something. Natascha does less damage, therefore to make up that damage you have to shoot at the person longer... which just gives them more time to kill you. It's probably more redeeming the more people you have around a Heavy, but since most people just run past the Heavy/Medic and ignore them to begin with it does no good and I ignore it. Natascha would most likely work well in an organized push with other Sasha carrying Heavies.
Shotgun because Heavies shouldn't run around by themselves and should already know where all of the Health Packs are to begin with. Sandvich is good for boxing on the bridge so you don't have to go back to spawn after you win.
K.G.B. because those gloves are ridiculous and going on punching sprees is hilarious (and effective if you have teammates with you and you can catch people off guard.)