If I were going to do cross-genre role playing, I would probably equip myself with d20 modern and future. Crossing it with D&D or Star Wars or most of the d20 lisence games would unbalance things, which is Rifts' biggest problem. You can do mages and tech guys with the rules, though you might want to customize some of the rules to make it easier.
The biggest sticking point about d20 modern is the economics system, which most people either think is brilliant or trash. I like it,because it lets me ignore things like taxes being due whenever in the game world, and I think it mostly works. It's not perfect, but it handles the vagaries of real world economics abstractly, not over simplifying it like a Gold Piece system would but not forcing me to calculate how mcuh interest is due on the character's home loan.
The other big issue, to me at elast, is that the magic is weak powered, generally speaking. It's not htat big a deal because it's universal and balances everything out. I just want to be able to plop a high-power archmage in the middle of manhattan.