I used to like booking.com a lot (before I discovered FT), and actually booked hotel with them a couple of times. Since I started FT I stopped using it because I won't get points for staying at e.g. Marriott. They have a big coverage of hotels, the site lists hotel policy very clearly (having 3 small kids travelling with us we need to know if we all can squeeze into a room without problem).

A handfull of times I used the site for Marriott LNFs, but for price wise they are not any cheaper than other online booking agencies. Very importantly they don't offer cash back and any kind of loyality programme. So if you'd like to book a hotel and see it somewhere else at the same price - would you still book from booking.com?