It's probably not going to make much difference which you choose tbh. Durham is slightly more famous around the world but they both have good departments. They're both in small cities but close to bigger ones. I'd probably pick Durham as having the colleges make it easier to socialize by breaking down the university into smaller manageable chunks (i.e. not just one big amorphous student union to socialise at... each college has its own bars/social events etc).
I'm not sure what this talk about plastic filled lakes is. Durham has a very nice river going through it, a few people drown in it every year which is sad but you can't see any plastic!