Booking.com and Expedia have customer service hotline which offers very good services and help in the event when you are facing issues.
My experience with booking.com was very good. The hotel I had booked with them was really terrible. Requested refund from hotel was rejected and since I booked via booking.com I complained with booking.com and ultimately a C.S. explained to me that hotel refused to refund due and on goodwill, booking.com gave me credits for next booking with their site. This was my experience and the C.S. did call back.
As for Expedia, it was about an additional charge which I didn’t know would incur in my booking. Same thing, I requested refund and C.S. took it up and refunded me after their internal reviewing. So I would say these two sites are pretty good in terms of C.S., having someone there to assist you when you needed one.
As for agoda, usually credit card promo very good. I booked with them at times and hotels usually are confirmed for my case.
I have positive experiences with the above 3sites
As mentioned by another that price may differ so simply need to check while they do offer cash back option with shop back as well besides credit card promos
Didn’t try hotel site