Basically, depending on the format.. (well go with 6v6)
In 6v6, which include class restrictions. [2x soldiers, scouts, pyros and snipers] (1x Medic, Heavy, Spy, Engy and Demoman)
Every war you will pretty much see the norm class picks, mainly Soldiers, Scouts, a Demo and a Medic. But depending on the map, some of these classes are changed to adapt to the map.
(
example could be, a heavy/engy to replace scouts on dustbowl, as dustbowl is a cramped map, which usually doesn't work in a scouts favor.)
Oh and which I like, only CP (control point) maps are used in GotGames and in other major comps. I really cant think of anything better to say.... Just join #tf2pug and join in on the action, best way to learn

or watch a demo *cough*
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