Worldwide? ATP is bigger than WTA and Murray's part of a 'cash cow' big 4 (even though he doesn't deserve to be part of an actual Big Four obv) so besides the USA where she's an adopted Yank and her homeland of Russia, I don't see where else anyone would pick Sharapova over any top 4 ATP. Not in Europe, or Asia.
China's only arsed about Li Na.
Yes, ATP is certainly bigger than WTA, but Murray is nowhere near the level of Sharapova on his respective tour as far popularity goes, while Sharapova is WTA's "golden girl" (with several slams, as pathetic as that may be). You may disagree, but I think she draws bigger crowds than Murray (unless he plays against the big 3, obviously).