A classic valve with a retro on-off will have the same trigger pull as a retro/X valve. It just won't have the trigger kick to reset. This leads to a shorter open time for the on-off between shots. The retro valve also dumps air into the front chamber directly from the valve input allowing faster recharge. Therefore, it is harder to short stroke a retro/X valve than a classic valve. A lazy finger on the trigger where a person doesn't fully release the trigger before pulling again, will be more pronounced on the classic valve. If you have well trained trigger fingers, then a classic is fine.
Except for the Automag in front, its usually the man behind the equipment that counts.