Medics are invariably invaluable, and demos and soldiers as well, but more heavy with the soldiers because they don't do nearly as much damage to themselves when they x-jump (x = sticky or rocket). Snipers can be a gamechanger with one hit kills (headshots) and have obviously the farthest reach of any class, plus there tend to be skilled snipers from lots of older FPSs, since it just requires precision aiming that can be gotten from other games. There tends to be a heavy too since the heavy/medic combo is very powerful, especially with no crits. Two medics would be nice, but there is the concern that you cannot protect both adequately.
As for my thoughts, I'm not really interested in doing any such - I don't care for trashtalk, and I'm not really interested in having any connection to atma after all the bullshit he has done combined with all of the chances he has been given.
A seperate challenge I have been issued though was by Optik (those of you who have been around for a while know who he is) - he generally plays with another community now that I guess he's a part of, but he offered a challenge of deFy regulars vs. OCR regulars, with 24 people on each side and matches of 3v3 for each game if I recall the details right (it has been like two weeks since he messaged me about this or something like that). If there's enough interest for this, then we'll do it - it'd be for fun, no pressure or anything like that.