Assuming the surface, conditions etc etc to be random (a surprise) I have to pick a guy who is consistent against most of them in tour.
Can't pick someone who is a complete mystery with lot of factors to be for his liking (Venue can't be in an altitude, Balls can't be lighter, Clay cannot be blue, Roof cannot be closed, Surface can't be pacy etc etc...)
So ---> Peak Federer would be my choice with full confidence that he could get the job done even if the surface was GLASS..