They are two very good offers.
Leeds is obviously the full 3 year degree course. From what I have seen so far it is a great course and their graduates are doing really well. It is also fully funded by student finance.
Mountview as an institution is arguably more prestigious but this is only the Cert Ed so in less than a year you will be auditioning again and there are no guarantees you will get a place on their full degree. There are also considerable fees to pay at Mountview.
Do you feel like you need an extra two terms before auditioning again or are you ready to begin your training proper now?