I know nothing about Liverpool, but as far as QUB goes:
It's predominately a local university, most students are from Belfast and other areas in NI, though its science/engineering based courses attract foreign students, and students the uk. I've heard a few English voices around so you wouldn't be totally alone (but still safely in the minority).
Aside from that quality of teaching is good, and there's plenty of bars nearby, do remember the weather is rubbish though.
*oh and you probably wouldnt get university provided accomodation past first year, but there is a large student community in the immediate university district living in rented homes, so its easy enough to get somewhere to live.
*oh, oh: and there's byzantine studies if you're into that sort of thing (arts students have to take a 2nd/3rd subject in first year).