I prefer agoda for all my online hotel bookings. If you travel alot & booked using the same e-mail/username, the points will add up, eventualy be enough to cover your hotel stay for your future trip. Had a bad experiance with booking.com because most of the time when you complete your booking process online, they will sent you a email confirming your reservation without charging anything to your credit card. The hotel will then charge your credit card 2 to 3 days before your arrival ( during peak season ). If there's something wrong with your credit card & the transaction did not go through, the hotel will proceed to cancel your reservation. Of course they will notify booking.com & a notification e-mail will be sent to you but at that point it might be too late to look for another hotel due to the peak season.
Well, that's what happened to me before.