Is it effective to vampirise during sex? If so who would be more effective at it, the penetrator or the penetrated? Or would there be advantages to both
Yes, it can be effective, particularly for women.
There is a sexual technique called the Big Draw, in which the woman draws the male’s energy into herself during sex. If done with malicious intent, the man can be drained quite rapidly to the point of unconsciousness (techniques like this are behind the myth of why men get sleepy immediately after sex, and thus why women were often demonized in patriarchal societies).
It is highly effective.
It is more easy to do it as a woman being penetrated, for obvious reasons.
It the masculine role, you have to refrain yourself from coming while your partner attain orgasm. You’ll have to use this moment to drain with the support of kinesthetic sensation, visualization and breath.
Sexual vampirism is one of the most exhausting practice of this type of magick.