This is a difficult question, because it's really dependent on the woman I'm with.
Some women have good control over their vagina and some don't. Some women are great at head and some aren't so great. Anal I've never been able to do since most women think I'm just too big and are afraid to even try it. Masterbation has lead to some pretty big loads and I'd say on average I cum more masterbating, but my biggest loads have been from vaginal sex.