Great Dover street is great, it has really good transport links, the rooms are nice, the people are friendly and there is a good atmosphere.
It is a 5 minute walk to london bridge and it's really nice to walk by the river or into the city if you feel like it.
It's expensive, but worth the money, and far better than intercoll's, most of which are waaaay overpriced and catered (dunno that may be a bonus for you, but personally i'd prefer to make my own food).
Stamford street are apparently good,most people put that as their first choice, but tbh i am glad i got great dover, i think i am happier here than what i would've been at SSA.
Every single person i have spoken to has liked their accommodation (even those in hampstead, which is really far out).
Depends what you are looking for in accomm and your budget i suppose.