I was choosing between these two. I agree, Norwhich seemed to have a better town that a lot i've seen but i still wouldn't think it was lively from my first visit, but maybe seeing it at night is different.
I'm putting Sussex as my first choice, I don't think you can beat Brighton as a town on your doorstep, i love it there! Music scene is amazing, gigs are wicked and all accomodation is right next to each other on campus.
UEA does get some really good bands at their union too though.