The Hulk is on another level than that of The Thing.
This isn't even debatable in my honest opinion, The Thing is a "teamster" and usually assists Reed Richards and the rest of the FF in defeating guys whom the Hulk would maul in a one on one confrontation.
The Hulk is marvel's top "tuff guy" hate it or love it(and in crossovers is usually pit against DC's top guy Superman, the Thing isn't even acknowledged in such cases).
The hulk has lifted mountains, survived nukes, limitless strength, beat down Gladiator(although controversial), beat down Thor, stalemated with Juggernaut, ripped off Onslaught's armor and much, much more. While the has merely said "It's clobberin' time", only to end up on his rocky hard butt every time.