The Best !!!???
It all depends on what you define as the best.
Here are the out of centricity data of some abex grades[*]ABEC3: 0.005 mm (0.000197")[*]ABEC5: 0.0035 mm (0.000138")[*]ABEC7: 0.0025 mm (0.000098")[*]ABEC9: 0.0012 mm (0.000047")

ABEC 5 would be a good smooth quality bearing. In most engines a #3 bearing would be excellent value.
ABEC 9 would be prohibiting in cost, but obviously better than the #5 bearing. Your engine however would not run better with it, unless you want to run it at 40,000 rpm</p>