St George's is only based at Newcastle on a part-time basis. Their main business is at Teesside. Northumbria is based at Newcastle permanently, with a base at Eshott.
At the moment, only St. George's offers commercial training, however Northumbria is busy preparing the CPL, MEP and IR courses. But I shouldn't think this matters too much at your stage anyway.
If you haven't already, I would highly recommend a visit to both establishments and meet some people. It will make your decision easier.
PS I am heavily biased towards Northumbria. If you want my unedited opinion then you can pm me.