others are right. there have been a lot of topics on this, but you show up and expect people to answer. So that kind of angers people, because this question was answered numerous of times. So I recommend using the search function on this forum.
But here is a quick and dirty answer. Most popular AP RO is probably the JF version. They just came out with a 15400 JF v4. This is the one you want to buy if you want to get RO. Don't get anything else. And only buy from TDs here.
If you looking for offshore, most common one and pretty good one is 15703 JF v9.5. If you want forged carbon 15706 XF v2 is your best bet.
So I just threw a few models out there, now using that info I recommend you search from the forum and figure out what you want yourself. If for any reason that's not possible for you, then just buy 15400 V4