I think a good isp is one that has good customer support. It doesnt' matter how good they are, if your site goes down and you can't get it back up fast and with help, you don't have a good isp.
Very true! We host our email on our own server at work and it goes down all the time and the "IT" person that is supposed to know how everything works takes all day to reply! He set it up in such an obtuse way that I have yet to learn the ins and outs of it (it's IMAP and I'm new to that). So customer service for any computer service is high on the list!