Neither, use your normal 2H main. Size doesn't matter nearly as much as everything else about the cube, unless you're already pushing your limits. (Which you aren't, because you're just starting out.)
Side note: It's very funny that people got scammed into believing the Tengyun v1 was a 55/55.5 mm cube just because it was good for OH. It's actually on the larger end (55.7-56 mm, depending on how you check) compared to its contemporaries, not smaller—its being good for OH was a property of its light turning and (relatively) weak magnets, not its size.