The correct answer is Silva-Weidman II (imo).
Silva-Sonnen II was big, but remember Sonnen was coming off a somewhat poor performance against Bisping (a fight I thought Michael won).
Silva-Weidman II there were two camps throwing insults at each other, and a controversial first fight... I mean that fight had it all going into it. Of course the fight failed to deliver in a sense.
I would say this fight is probably #2, in relation to the other fights mentioned. DC is coming off a dominant win over ol' hot and cold Hendo. Jones dominated Glover in his last fight. Both guys undefeated (*). So tonight has to be way up there.
A few other big fights not mentioned in the poll were Chuck-Tito, Tito-Shamrock, Lesnar-Carwin, Silva-Belfort, Couture-Liddell II...