If you can....GO OTC!
I started university 4 years ago with the idea to join the RAF as an Air Traffic Officer, and I was told that UAS on the whole, only really catered for pilots, as the rest were "just groundies" (may not be entirely true, but I've heard now that flying times are being cut, and generally a lot is being cut).
So anyway, I joined the OTC and it is by far the best decision I have ever made. The 4 years was immense. And I'm still joining the RAF after it - the army tempted me a bit but I'm still staying blue.
Good things about OTC:
1) Generally more people, with more diverse interests. There are still many Navy/Marine wannabes joining the OTC for experience.
2) You get paid more. Simple. You get a pay rise after you get certain qualifications, and the limit on the number of days you can earn is ALMOST limitless. e.g. Last year I managed to clock up 99 days. At £40-odd a day, you do the maths. UAS I believe get payed less, and have less numbers per year (I hear it's around the 30 day mark)
3) The army is a bigger organisation with many different corps and branches. Therefore, there's more money floating around to give you the chance to go on different courses, trips, etc. I've been skiing (yes, i know you can do that in the UAS) but I got my army qualifications, parachuting, mountaineering, white water rafting, kayaking.....I'm a qualified Artillery Command Post Controller, I've done field engineering, signals officer courses..... I've even done the US army commissioning course for fun, as part of an exchange. All paid for.
4) Being in OTC generally means you have your own building in a barracks, and doesn't mean you have to travel to an RAF base all the time. You therefore make closer friends as you see these guys a lot of the time.
5) You get to see how another force works. At OASC, the interviewers seemed dead impressed about my knowledge of the working of the army...above that of my already-gained knowledge about the RAF. You can't learn that type of experience just by reading about it.
6) You get a good lot of field leadership and training experience. You are constantly in positions of command, looking after the younger ones etc. For my final year I was in charge of my own platoon, which lets you really learn about how to look after your troops welfare (you are the one that sorts out pay problems, uniform problems, writes their reports....lots of stuff). Again, all good experience for the future, and certainly I do not believe you get that amount in the UAS (my UAS mates have told me).
7) Social functions are so much better :P
So on the whole, in this day and age of budget cuts, I still think the OTC wins hands down for a good time at uni. I do know that the OTC now is focusing more on army officer recruitment instead of just giving "students a good time on the taxpayers money". However, after a brief leaving chat with my CO, he still says that he would be interested in recruiting future RAF/Navy officers, as they bring "something a bit different" to the OTC, and he knows that in the end, if you put you're all in it, the OTC provides you with invaluable experience that cannot be gained anywhere else whilst at uni.
Hope that helps...