The 55X is a very nice table. So is the 570. They both have their strengths and weaknesses. In sheer bulletproofness, the 55 might get the edge -- the 570 has some weak points that will fail eventually. But the 570 has the better arm, and arm height is adjustable. And the 570 has quartz lock and better specs.
You can't go wrong with either one. It's like saying which one is better...a 69 Camaro or a 69 Corvette...wouldn't throw either out of my driveway.