Isn't Superman weak to magic and enchanted items according to the comics? He can be cut by Wonder Woman's sword so in the Bonus round, Thor could potentially defeat Suprman with his Hammer

For round 1 team cap has Scarlet Witch who has the potential of holding down Superman in a bubble letting the others take him out. However it won't last long and in the end DC will win however if Scarlet Witch manages to mess with some of their minds, she could possibly turn Superman against the team. Also we don't know wether or not anyone is given prep time, if that's the case Hawkeye could prepare Kryptonite arrows. Also since it was revealed in WW that the Amazons can get killed by Bullets, a well placed shot by Hawkeye could possibly defeat Wonder Woman if she is too distracted to block. Also don't forget Antman, he could potentially throw out his shrink discs causing Superman to become really small and letting Scarlet Witch hold him in a bubble

For round 2, the Vision can take on Superman, they both however will probably not end up defeating each other. If prep time is included Iron Man could use Kryptonite. Also keep in mind that both Ironman and War Machine are on this team so it would be like 2 armoured Batman in BVS going up against Superman.

For round three, based on round 1 and 2 above, the Avengers would win