Murray has a better chance than Tsonga to win one in 2012, but I wouldn't be surprised if Tsonga has a bigger chance to beat one of the top seeds 'easier' or 'before' Murray.
Nadal will get beaten by Djokovic at any slam
Djokovic will get beaten by Federer outside of the Australian Open
Murray will get beaten by Nadal at Wimbledon
...so whoever can leak through that.