Best hotel booking portals?

For our just completed trip to Poland and Czechia we essentially booked
everything through booking.com. Was ok, but for instance in Cesky
Krumlov I saw many pensions with signs 'rooms available', while when I
booked Pension Antik it seemed to be one of the few alternatives
available. Which makes me wonder if booking.com is perhaps listing only
a subset of the accomodation available. Which hotel booking do you
recommend?
--

Alfred Molon
http://www.molon.de - Photos of Asia, Africa and Europe
.