Depends. If it's only been a bout of outercourse, tits. I love tits, and I like seeing my load so that if it's big, I can feel proud of it and if the lady is so inclined, receive a compliment or at least giggly remark on how much there is - that's fab. It is a great feeling of course to receive a blowjob to completion, but I prefer not to cum in her mouth or on her face in case she is only being nice and actually doesn't like the taste, or for risk of getting her in the eyes for facials. Tits does nicely. I did however have an ex that if I woke up horny, she liked me to wank on her arse. She did have a nice arse though.
If we have sex, if I've had to wear a rubber then I like to pull out and cum on her tits, especially if she yanks it off. However if I've been inside her without a condom dulling my sensitivity to the feeling of tight/wet/warm, then I can't possibly pull out. To paraphrase a great man, I couldn't stop if a meteor hit me. I've had enough girls tell me they like to feel it throb inside them when it goes off, and there is something sensationally hot about looking into a girls eyes while they feel you coat their walls with liquid love.