Honestly, all of them.
Cumming on a pair of boobies is fun and all especially as a conclusion to outercourse, but ultimately if I'm inside a lady and feel the little white army threaten to start their march, the last thing I want to do is break my rhythm and pull out. The best thing in the world for me is shooting into a lady, especially in face to face positions, looking into her eyes either in missionary with her muscle clamping around my cock and legs tightening around my waist, or her on top, riding me until her joy division forcibly extracts my liquid love. It feels best for me.
Plus several ladies I've been with say they like to feel the throbbing/pulsing of a cock going off inside. Sold!