What Flash said.
You're not the first to be lured by the "OCS gets you a guaranteed flight billet" idea. Don't focus so much on what is "guaranteed" or "better chance", because as has been illustrated, nothing's guaranteed and chances are impossible to asses.
If you want to talk about guarantees - ROTC contract means you'll graduate with no student debt and a guaranteed job. Right now you're probably looking at that and thinking, yeah, but what if it's not my dream job? It's still a job, and those are getting harder and harder to come by for new grads. Very, very few are graduating and finding a job in any field. It's not like the movies where your hat hits the ground and the next week you're VP of Social Media with a bitchin' Manhattan loft. You're more likely to be working a very low-paid, disposable job and a couple hundred grand in the hole. By comparison, even being a Shoe isn't too bad. Any officer job in the Navy is reliable, well-paid, good on a resume, great benefits, and gets you training and experience.
So in short, by dismissing ROTC as an option, you're rolling the bones on what you'll be interested in and qualified for - and how many dudes OCS will be taking - a few years from now. If ROTC doesn't pan out and you want to keep OCS in mind as another way into a commission, fine, but just not trying for it because you think it's a better chance to get exactly what you want is poor headwork in several ways.