(Also mentioned in another thread) I have all three, all on competition pistols. I like them all. If I HAD to choose one, it would be the 507Comp, but I'd be happy with any of them. As well as would recommend all of them to new(er) shooters, whereas some more experienced shooters may have preferences in the details that each offer.
I thought the larger 5 MOA of the XL would bother me. However, after a handful of matches with the XL, I haven't noticed either way. It really isn't that much different than the 507Comp (2 MOA) and SRO (2.5 MOA) during a course of fire. I do notice a difference side by side, but for practical shooting, I'm good with either.