I'm with Tiscali, the 1mb unlimited at £14.99 and I've had no problems with the connection at all, it slows up a bit sometimes but I think they all do that from time to time.
The only problem I did have was when I first started they would forget to bill me one month and then bill me for two months the next time. Took me a while to get it sorted but now its fine. I found their customer service/billing to be rubbish, they didn't answer the question I asked and that was very frustrating but their technical helpline I found to be good so its swings and roundabouts as far as I'm concerned. Overall I'd recommend them and am happy with the service.