What is the best website to complain about a hotel that gave very poor service?
Most hotel's have a website try searching the hotel name on google to find their site where you can post your reveiw. If they do not have one I advise posting it in the newspaper or telling the hotel directly. Complaint sites are usually ignored.
The biggest and best site is http://www.tripadvisor.com/
Some others...
http://www.yelp.com/ http://www.boo.com/ http://www.resideo.com/
And, of course, contact the hotel (the actual hotel & the chain headquarters).
Go directly to the hotel, as they might reward you with a free night stay or similar because of your horrible experience.
There are severa options:
The Better Business Bureau website
complaint.com
and epinion.com
Here's one of them: http://www.complaints.com/
Good Luck !!