It would be best if it had teams and roles, and balanced accordingly. Fuck KDR and W:L. This way cav would be against cav; and similar numbers of cav, archers and melee on each team. If they're balanced on their effectiveness, they won't really improve if they're distributed randomly. If this doesn't make sense to you, utilize your peanut brain (not peanut head) and think. A noob cav fucks over a noob infantry, but is bent over by a noob ranger.
E.G.
Choose Team:
-------------
Red Team
Green Team
Choose Role:
---------------
Infantry:
Archer/xbow:
Cavalry:
PK:
Then it'd be filled out accordingly.