I always thought that the BEST version of Murray is when he is playing aggressive AND playing aggressive defense at the same time! What is so ironic about my statement is that he does on his worst surface!
On grass, he is aggressive and plays aggressive defense but most of the time he just use his variety and slicing ability to throw his opponent off (and it perfectly works).
On hard courts, sometimes he is not aggressive at all!
In my opinion, the reason he has gotten better on Clay is because he finally realized he could be both aggressive and play great defense at the same time on this surface.
And that is why right now he is ahead of Wawrinka in this match. He is playing great defense to make Wawrinka hit an extra shot AND he is aggressive enough to make Wawrinka move around the court.