I'm completely biased seeing as I go to UEA, but I'd definitely make that your choice. It's a lovely university and all my friends doing maths all speak very highly of the course. Having said that, you might want to spend some time checking through the modules and degree programmes on offer at both and see which one best suits your interests - it's better to do a degree better suited to you rather than do a less appropriate programme at a university with a stronger reputation.