I would also say that depends on who you are fucking, but I would say that lifting is consistenly more rewarding to one's self than sex. Now love thats a different story alltogether.
Thank goodness it doesn't have to be one or the other. In the real world, I have great workouts AND great sex ...
I used to manage a gym, one time I brought my then gf in after close (actually there was one person still tanning, but they don't count) and we re-enacted our own version of pumping iron I must say, sex amongst the weights was pretty damn good -- a nice blend of my two favorite things ... Nothing like watching nude flyes on the pec dec.