http://www.hostingassured.findmyhosting.com/ -- this was a GREAT site years ago. It allowed people to review their host. The IP numbers were verified that the domain was actually WITH the host before the review went public. Hosts were unable to remove reviews (only comment on it). The system, while provided by a TOP HOSTS site, was actually pretty great, however in recent years their forms broke and they never fixed them. It gives a pretty good unbiased opinion as hosts are unable to edit anything - gives you a better testimonial.
As for best and worst - these are judgement calls. Much like I can't say that FORD has the worst car ever, and Chevy is the best truck. These are judgement calls. THOUSANDS of people love them, and thousands hate them, all for different reasons.
As mentioned, the more customers someone has, the more reviews you'll find (good and bad). People like to post BAD reviews more than good reviews. This is human nature. If you have 100 clients and you have 10 bad reviews, is that good or bad? 90% success rate is good in most businesses. So if you have 10,000,000 customers, and you have 100,000 bad complaints out there, isn't that still good?
As you see, a cut and dry list is hard to do. Spammers on the other hand, that's very easy to pick out. If they spam, they are blocked. End of story. But when someone claims there's a spammer, and there's no way to back it up, what can you do?