Just to add something...
If anyone, I'd have to agree with TicklingDuo-Drew and say that the Undertaker would probably fit best. His big thing since turning heel has been "Respect my seniority!" and "I'll make you famous!" This sort of thing would fit in well with the big-headed superstar personalities of the nWo.
At the same time, however, Undertaker is such a big star that to have him join the nWo would probably be a downgrade in marketing. I mean, how much money must have been spent on entrance music for the Undertaker? First his theme was done by Kid Rock, and now Limp Bizkit. They'd be tossing money away to have him use the nWo entrance music. I don't think Vince MacMahon would go for that.