If you are getting a new cylinder from Honda, then you run the A piston. Best bet is to get the cylinder, measure the bore and then order the piston. B piston is the next wear at .01" greater
If you are going to send it off to get sleeved, then buy a piston A or aftermarket like a wiseco and send it with the cylinder. You most likely have the option of buying a piston from the people doing the sleeve of the cylinder also. But they have to be matched up for the correct tolerances - which the shop will do for you.