If you really want to be a pilot and don't care which service you join I would suggest going Navy. They have the best chance of becoming pilots of any of the ROTC programs. For example almost a third of all commissionees recieve a pilot slot in the Navy whereas in the Air Force the competition is much fiercer for fewer slots. Of course I encourage you to go Air Force anyway!
Air Power!!!
Regardless of what you decide to do, your three top things need to be grades, proffessionalism, and physical training. Your GPA, how your PAS ranks you compared to your class, and your PFT scores are going to be the top decisions in how you make pilot. (oops forgot: as well as how you do on your BAT test)
Oh and while it does give you an edge if you have a private pilots licence it's not going to balence out the other things being bad. I happen to know 3 lieutenants who made pilot without private licences...they just had to delay training until they had received them (and the AF paid for it too).
Interestingly enough the difference between the last pilot slot recipient and the first non-receiver was less than .1% this year. That means if he had run 3 seconds faster, done one more push-up, or had a GPA .01 higher he would have had the slot.
Another option you can consider is that those who have technical majors besides having better scholarship chances

can also go to test-pilot school. Plus you could also try for a Nav slot!
Hope that helps! Good luck and do your best!