I've been with Dreamhost for 3 years now and am very satisfied. I don't really have anything to compare them with, but it seems to me that they have an unusually good vibe about them. Good customer service and a generally nice attitude.
And now I will be the first to post a shameless
referral link to Dreamhost 
Although I think you actually get a better offer through a referral than otherwise, so it may not be entirely self serving. *ehm*