HHonors site is the worst - I have to log in multiple times when I want to use it and I have no idea why. Plus it's hard to filter for all hotels in a city with a specific rate code or promotion available.

PC's is pretty good for my limited use - I used it recently to set up my two "Crack the Case" stays and had good success filtering on a specific brand or the "quality rating" for a city. (Let's be honest - if you gotta do a Saturday night at a HI/HIX type place, you want to filter on a "quality" rating!!) Of course, I have no idea what PC's quality metrics mean or whether they really correlate to the better properties... I like being able to hover over the map and see the hotel name associated with a point. For example, if I filter on Quality for Dallas, it shows about 50 points on a map with point 1 being the highest-quality-rated hotel.

I've always liked Marriott's site, even though the latest redesign is a big performance hog and a bit hard to use over a mobile 3G connection. Starwood's is in the middle somewhere...clean, attractive site but sometimes shows rates and availability on the initial page that aren't really there when you click on the link. (For example, I keep seeing C&P available on certain properties - but then you actually click and there it's unavailable.)