I honestly just use every tool I can when trip planning: Google, Booking.com, airbnb when applicable, Expedia, Delta trips, even my credit card company has a link.

Similar to the other responder, I think Booking.com had the best dataset for some random features like a hot tub (specifically big hot tub, not bathtub). The problem is that it only searches for hotels with the big hot tub, if you want that actual room you usually need to book direct.

It also yielded some good results for Japanese ryokan (traditional spa hotel), more so than the other search engines. Google is fine as well but tends to lean more towards big hotel chains IME.

Not saying its perfect (nobody does ryokan well at all), and the more familiar I get the more I'll tend to book direct, its just one search tool out of many. If it went away tomorrow I wouldn't miss it terribly.