It depends on the type of tourist you are. My mom would love to have a knowledgeable guide explain every last detail. I'd go nut's after about the first 10 minutes because I like to wander at my own pace and not be bothered. Drivers are good because you need transportation, they are cheap and best of all they have air-conditioning. Another thing about Cambodia. To me, it feels kind of rude or arrogant to leave a driver sitting around in the hot sun all day while I take my time and meander about. It seems like I'm wasting his time. But in reality Cambodian drivers would like nothing better than to wait around for you as long as you like. They get paid the same and aren't burning there very expensive gasoline.

Last time I was there I hired this guy because an awesome driver I know in Phnom Penh referred me. I can't vouch for the rest of his services but as a driver he was professional and had a really decent car. IIRC $25/day flat rate.