I know you have made up your mind where you are going but for future reference you have got to take a look at Newcastle and Gateshead. I have visited lots of places in the UK and IMHO for the best night out you will ever have there is no where quite like it!
I've done Newcastle... for a stag do. Had so much fun. And actually that's the spirit I want more... the last two places me and my friend went to (Cambridge and Bournemouth) were dull as ditchwater... so we want something where something more will be happening, but with things to do in the day (so York can fulfil that, as Leeds doesn't seem to have masses to do.)