I have had experiences during both sex and masturbation where it felt like my entire life flashed before my eyes in one second. And, to quote American Beauty, "that one second isn't a second at all, it stretches on forever, like an ocean of time….And then it flows through me like rain, and I can't feel anything but gratitude for every single moment of my stupid little life."
Some have commented that sex has a whole other emotional side to it, but as you can see, there have been times during masturbation when I have experienced the intense emotions as well as during sex. Although sex may be more likely to involve intense emotions, it's not guaranteed. Anyway, I think that for me, as long as the physical side of either masturbation or sex becomes intense enough, the emotions hit me as well.
In fact, I have also had experiences with both sex and masturbation where it wasn't that great at all, and was kind of disappointing both emotionally and physically.
So, the fact that I've had times during both sex and masturbation where I was in awe of the universe, and times during both that were disappointing, makes it difficult to compare the two acts. Either one can entail such a range of experiences…