Most TA units draw recruits in from a wide range range of backgrounds - in my TA squadron we had lads who were casual labourers through to the landed gentry, with and without titles. Once inside the gates we pretty much left all that behind, and the craic was superb. The regt had a very real role in the wartime orbat, and that was a massive motivator.
OTCs on the other hand are at worst a drinking club, and at best they'll never be a fighting unit. By definition all the guys and gals will be undergraduates aged 18-25. You'll mix with them and their type by being at uni, but you won't meet the lads I mentioned above in the OTC.
The fact that you've served in the ranks should be very useful as a baby officer - you'll learn loads and it will show.
As mentioned, if you put the effort in, it will be re-paid - both in your wallet and your experience.