What's better

Well, that would be a psychological stimulation, not a physical one. Normal human psychology dictates that pain hurts and pleasure feels good. Anyone that derives pleasure from pain is recieving a psychological form of satisfaction from it, not a physical one.

Here's a converse example of the same thing I'm talking about. Let's say you go to a a party, get super-drunk, and end up passing out in the middle of the action. You wake up, and when you open your eyes, you realize that you're being unwillfully fellated by the nastiest chick in your highschool. Diseased, filthy and just generally unattractive. Mentally, you are revolted. Physically, though, if you weren't aware of the identity of your "attacker", you would enjoy it. However, since you do know the identity of the person performing oral sex on you, that drastically affects any pleasure you may derive from the act, making it completely unenjoyable.

The same applies to anal sex for women. There's no possible way for a woman to derive actual physical pleasure from anal sex. There are no sensitive errogenous zones located in the femal colon, they don't have a prostate like men do. Therefore, the only way they could derive pleasure from it is if they enjoy pain, which would affect the physicality of the experience for them. It would make a normally unenjoyable physical experience into an enjoyable psychological experience, just like the situation I described above would turn a normally enjoyable physical experience into a thoroughly un-enjoyable psychological experience.