I had a specific set of places I wanted to visit and Ms. Sokun Lin the general manager at Happy Angkor Wat Tour, was very helpful and patient. I went back and forth with my requests and I was given an itinerary that fit my timeline and my interests.
My guide/driver was Mr. Veasna (a Khmer version of the name Vishnu) who was very knowledgeable about the places we visited. The other awesome characteristic in addition to his extensive knowledge was his ability to predict the best times to visit the places I wanted to avoid crowds and get the best lighting for photos.
All I did was sit back and listen to him tell me where we were going next (in an air conditioned Toyota Camry) - he would then draw the plan of the place we were visiting on the ground (if warranted) and when we were done - offer me a cold towel and cold water (you have to be there to know how much of a relief these meant...).
He picked me up at the airport and dropped me off at the airport at the end of my 3 day visit. He was always early to pick me up at my Hotel (also awesome - look for my review). He advised me about the food and buying souvenirs etc. We spent a lot of time discussing the places we were visiting and the carvings and sculptures - which were based on Ramayana and Mahabharata and a lot of Indian Epics and so called mythology. His knowledge is extensive and I learned a lot in our discussions.
I would and am already recommending this tour company and my guide to my friends who want to visit these wondrous and awe inspiring monuments to human achievement.
Have a great time and read up before going to Siemens Reap. It's a privilege to see these so go prepared to be amazed.