As previously noted, the main difference (other than than price) is the location of the safety. There are two schools of thought, those who use safeties and those who don't.
You must determine how you plan to store your HD weapon, and many factors must be seriously considered: Some store their HD guns fully loaded and ready to go with the safety engaged. Prior to firing, only the safety need be disengaged. Others chose "Cruiser Ready" with the magazine loaded, the safety off, and the hammer down on an empty chamber. To fire, first the action must be cycled, but with no changing of the safety.
With the first preference, operation of the safety is critical and many proponents prefer the location of the 500's thumb safety. With "cruiser ready" the safety isn't used and some consider a thumb safety a hindrance. After due consideration, my preference is the latter, so I would select the 88 over the 500. Your preference my differ, if you plan to utilize the safety, the 500 might be a better choice.