There's another option - join the TA. Great experience, proper training and access to courses, really good bunch of guys and gals normally, and you can't be mobilised until you have graduated, by which time you'll have resigned and got through OASC....
Stay in the ranks, easily make Cpl in three years, really good grounding in military life. OTC is a bit girly, really, IMHO.
A number of mates successfully went this route while at university. One ended up as a Chinook pilot.