I think I did over 200 bookings at agoda over the last few years. I also did a few bookings at booking.com. Both have great bargains every now and then. I usually end up with agoda as they tend to have better prices with hotels in Asia. Booking.com however is the biggest hotel site in the world, but price wise agoda usually has the better offers (in our case).
What I always like is the fact that hotel operators understand the importance of a good online reputation. Whenever I mention I had a reservation at agoda or booking.com I feel like they offer a slightly better service as they know you are active online and that means you are able to leave reviews