Me personally, I would go with long term relationships, they offer so much more then a consistent string of One night stands.
A good fictional example is Anthony Dinozo on NCIS. At the start of the series, he was a "Swinger" by the definition of this thread, and by the end of third season, he meets a nice Doctor lady, he falls in love with her, they start looking at houses together, he meets her mom, and then he meets her dad...
click to show spoiler
Who turns out to be an international weapons dealer who he's been hunting for 2 seasons.
...And he seems happier for it!
And for those 2 people who voted "Both", you can't have your cake and eat it too. Its either one or the other folks... unless both of you are into that kind of thing, then all the more power to ya.