AR15 advantages include accuracy, spare parts availability, aftermarket parts availability, easy to mount optics, easy to further improve accuracy with match barrels, match triggers, free float handguards, etc., increased range of projectiles, easy to field strip or even further and clean/inspect/lube.
I know many people will say AR15's are reliable but mine seem to do pretty well.
Good ammo is easy to find. Brass is reloadable. Components for reloading are easy to find.
AK47 advantages are pretty much the acceptance by almost everyone that it is more reliable than an AR15.