Becky,
if money permits why not do both? It will take dedication but having spent 4 years, scottish uni, at uni and only just getting into flying now, I wish i had gone down this route. You can get your ppl done quite quickly if you are dedicated, 4-8 weeks in usa, and with the uni holidays thats feasible. failing that the first year of uni would allow you enough time to fly at the local flying club at the weekends and hence you should have a ppl before your first year of uni is over.
The atpl's are harder to fit in, and a bit riskier. The reason is the 18month to pass all your exams from first exam sitting. Having said that, once again the first year of uni is not all that hard, so if you got your ppl knocked out in america in 2 months you could get a distance learning ATPL course and be sitting your first set of exams in around feb, just before starting your study for uni exams. I don't know what course you would do at uni, but for me, science based, most of my essays were based on lab work i had done, and hence the time was consumed in the lab, and not so much with my head in the books, this changed in my third and fourth years though
Uni's know that most people have a good time after class, and whilst don't seclude yourself from the world it may be that study will consume your life, not alcohol!
Then after your uni finals, should be finished in May you have till October to finish off your ATPL's before uni starts back, and this means the August sittings for the second set and october sittings for any resits is possible
Then weekends for the CPL, night and hour building before doing your IR in your second year holidays. Now you have 2 years of uni under your belt and a frozen atpl, keep yourself current but focus on your final year of uni.
This is a hard option but if you want both its an option.
For me i wish i had done it this way, however hindsight is a wonderful thing, and up to know my path would be different if i had a chance to change it. However would i have been dedicated enough, would i have messed both courses up and ended up with nothing? As it stands i'm 3 years older than when i left uni but i do have an honours degree and am close to adding a cpl to my CV