2PM and Wonder Girls for me ^^ I'm pretty overly bias towards Wonder Girls so maybe that's why I think they suit them more mrgreen . SNSD and kara I think is too cutesy for them. The grace is more suited to singing, not dancing (since 2pm dances so well). truthfully, i think sm wouldn't let them collab with anyone besides their own entertainment cause that's just how sm is.... have you guys noticed that? its usually collabs with famous veteran singers....
4minute.... just no.... they can't handle 2pm.... and 2ne1, if i wasn't bias towards wonder girls, then they'd be the one ^^
and i don't know much about the other groups to criticize them xp