The answer is "none of the above." The alternatives A, B and C that you have offered are all backward-looking. But sex is forward-looking. I'm sorry to be a materialist here, but biology is more enlightening than all the divine revelations or human reasonings that we could bring to bear on this topic.

Why does sex feel good?

Allow me to suggest a cursory study on the latest research on oxytocin, the "commitment hormone" that comes into play in key pair-bonding situations, including intercourse and nursing.

Why, one could ask both rhetorically and really, would a pair-bonding-promoting hormone figure into these scenarios? Coincidence? After a million years of evolution, I doubt that it is either inconsequential or coincidental.

Here's the thought that always occurred to me: "What next?"

In pondering that question for years, I was not satisfied with the obvious response: "On to the next fuck!"

I kept asking myself "What did I just experience? What did I just do with this other person? Call it pleasure, but where did the pleasure come from?" Call me a materialist, but I refused to believe it came from some overhead eternity. And I refused to believe that it was an arbitrary construction.

And again, "What next?"

Oxytocin is neither a simple nor a superficial resource in dealing with this question. I know that what I just experienced had something to do with pair-bonding. I feel bonded to this other person. For how long? For richer or poorer, in sickness and health. If that's too hopelessly romantic for you, how about "just long enough so that this other person doesn't feel like they've been fucked over."

That, friends, is the "sexual experience that is more satisfying."

It does not bother me that this whatever-it-is did not come about via my rational choice -- that it is in some deep sense "beyond me." As I said, a million years of evolution means something. Our bodies may not have been divinely dictated (in the pre-modern world view), but neither are they self-constructed or even socially constructed (in the post-modern world view).

...

Or consider A, B and C as stages in a relationship. There has to be a first time, which is A. Maybe there was a second time... and if you weren't paying much attention, you thought it was "just B." But if you're doing it beyond that, either you've reached C... or you'd better move on to a new A, because that relationship ain't goin anywhere. And next time, consider what I said above. If you're at A, and you're not thinking "What next?" then ask yourself... "Am I fucking, or just fucking somebody over?"