Frankly, I think any city will have a hard time beating Cardiff on the indie scales.
It's small, it's a bit of an outsider compared to other cities, and for these reasons it has so many cool things to show for that you wouldn't bother with in bigger cities - and you don't have to travel far for any of it.
People who know Cardiff will know what I'm talking about - Clwb Ifor Bach is obvious, anything that ever happens at Milgi, the Sunday Sinema at Buffalo's, Spillers, the motherfucking Swn Festival, the arcades with all their weird stuff, etc etc etc. Plus because of its small size you're likely to run into many of the same people at several of these things, which creates a nice feeling of elitist community.
First person to say London loses everything ever.