Sex with a partner is 400% better

[watertank]

Surprisingly, after orgasm from sexual intercourse, the increase in blood prolactin levels is 400 per cent higher in both sexes compared with after orgasm from masturbation (Biological Psychology, vol 71, p 312).

This explains why orgasm from intercourse is more satisfying than masturbation, says Brody. Since elevated levels of prolactin have been linked to erectile dysfunction, this may also explain why most men need a recovery period after sex.

http://www.newscientist.com/channel/sex/mg18925405.900.html