I just love booking.com. I use it for all my travels - around the world! I reached some kind of Genius level and it gives me even more discounts. Very pleased.
My friend told me about Ozessay last semester. Before placing an order, i talked to their support first as I was looking at several services. A very nice lady answered all my questions, and I was pretty much convinced to go with them. I have since then placed several orders with them and i am overall happy with my results.
I like using orbitz, but they should really do something about all those ads (and add-ons). Can be confusing to use. But i usually go with them since they offer good prices.