I would just say that booking.com seems to charge more with 'free cancellation' than they do when they offer the same room without 'free cancellation'.

But I do use FC and then a week out from the day of stay, look for the same room and if it is available at a lower rate, cancel and rebook.

Did that in Spain last year.

As previously mentioned, trivago.com is a good site to compare the different sites prices.

Silvia - I find I usually don't have to pay anything up front when I book directly with the hotel. They will ask for a CC to hold the booking, but all sites do that. I actually am booking a hotel in Bern that doesn't ask for CC info unless I want to insure that my room is held beyond 6PM of the date that I am supposed to check in.