I think Murray has the better first serve, movement, overall defense, and net game personally. Backhand, return of serve I would call a virtual tie, but if one wants to give Nalbandian those then fine. Forehand probably Nalbandian, although I dont think either has an amazing forheand, and probably second serve Nalbandian. The huge difference between the two is fitness, commitment, and desire. Granted Murray is a bit of a choker in big matches, but he still gives his all to his career, which Nalbandian never did, even when he went through long healthy droughts. There is no excuse to be carrying a big gut like that around most of your career, just like Serena's injuries dont excuse her frequent lack of fitness, but in her case she is such an insane talent per gender and the WTA has also fallen apart so badly of late she gets away with. Murray's 8 Masters titles, 3 slam finals, many slam semis, and consistent top 4 ranking sets his well apart from Nalbandian who never had the day in and day out consistency or focus for such results. JMO of course.
Dont get me wrong though, I definitely understand those who think Nalbandian was more technically talented despite his inferior career.