Never sucked cock myself as I've never been in a serious enough relationship to do anything unprotected (well, never actually been in anything that would constitute 'a relationship'), and am extremely averse to the idea of a mouth full of latex. However, my guess is that I'd probably swallow as spitting would involve having to clean up the mess (and you'd still have the residue in your mouth). As for fictional characters: well, from what I recall I've thus far only written blowjobs from the PoV of the character on the receiving end of things. However, when I contemplate the matter it varies from character to character. I picture Crowley & Aziraphale swallowing, but think that Draco Malfoy would definitely spit (though I'm sure that his Malfoy ancestors would be appalled at this blatant disregard of, erm, etiquette).