I was in the exact same position as yourself and elected to try for NATS whilst my university applications were being processed. A job offer came before the university offers so I took that.
Now almost 5 years later I have no regrets. I have enough time off work that I can still indulge in the university lifestyle with my mates for much of the year and whilst many of them are now on the dole with frankly useless degrees and a heap of debt, I'm bringing in a rather sizeable salary for my age.
I'll go against the grain and suggest having a go at joining NATS first. The younger folk seem to have a much easier time when training and should you not make the grade, you'll still be young enough to go to university and indebt yourself. If you do make the grade, you'll still have enough time off work to enjoy the finer parts of university social life without the baggage that goes with it.