Generally speaking all dating sites suck for guys. That being said, OkCupid seems to suck somewhat less than the others, and if you are only using the free version of the site then it's worth putting up a profile, as long as you don't let yourself get hooked on it and start checking your profile for more than a few minutes every other day.
I've had far better luck with the site meetup.com, where you actually get out of the house and meet people who have similar interests. The "sit-at-home" dating sites are just not an effective means of finding a date.