Clearly Murray. By a considerable margin. But Nadal is mentally and physically stronger and has more power in his game. And that's what counts in majors. So if you asked me who would I take in a GS final, I would pick Rafa every time for those reasons alone. But at their best, Andy is the player whose game naturally translates to the surface and match-up with Nadal much better.
OK, leave out majors. Just what results in 'minor' tournaments has Murray achieved that place him so much above Nadal? Indoors, I would agree, but outdoor hard? He hasn't won more MS.