My husband and I lived in Cambodia for a year as Peace Corps Volunteers. We lived about an hour and a half from Siem Reap in a rural village, and this is where we always stayed when we came into town.
The staff is amazing, it's two cousins who run this and the hotel next door, and they're sweet as can be. The rooms are always pretty clean, especially for Cambodia. There's also pretty cheap. I think $7-8 for fan and $13 for AC. Sometimes you have to remind them to turn on the hot water in your room, and the most commonly broken thing in the room is the shower head, so make sure and let them know if it isn't working.
The hotel is just far enough from pub street area that it isn't too loud, but it's close enough to walk to pub street and all of the markets. My favorite market is just across the river from Angkor Park Guesthouse.