I always use Bliss Travel Service
I called Bliss to assist with the land portion of my London trip because I've used them before for 2 European vacations. They (usually Dominique helps us) always have great suggestions for hotels and they have also been able to save thousands on hotels and transfers. I didn't even ask them to find discounts, but they quoted me for a hotel (king premium room) and transfer from airport price that was $1500 less than what I was able to book on my own for hotel only! They even set up a nice surprise in our hotel since it was our 20th anniversary. I highly recommend working with a travel agent, especially Bliss Travel Service for big trips! They have access to options that we don't and knowledge that we don't. I highly recommend Bliss Travel Service.