I've never had an ISP that I've liked since the dialup days. I remember liking a couple of the ISPs that I had at that time a lot, but EnterAct in Chicago is the one I remember most distinctly. They were very transparent about what was going on, provided great service, and did things like offer different numbers for different 56k protocols so you could get the best speeds and stability depending on which modem you owned.

Unfortunately EnterAct was eventually sold to some larger company and DSL became more popular.