You could technically find best build, one that can clear most ubers with certain set of items and skills. Not that game is so balanced, such thing doesn't exist.
And if you look at entire characters (so respec and gear swap allowed), there there is definitely big differences between ubers viability. At certain level of gear pretty much every class can complete all ubers, but there will be big difference in how easy it is to achieve, and what kind of level of gear is required.