If you're going to consider living in Phnom Penh, the neighborhood where I
lived was near the Russian Market and I would highly recommend checking the area out. It's not as filled with tourists like the riverside and it's not as expensive as BKK. I really liked it because there are a handful of Western restaurants, you can buy almost anything you would ever need at the market, and the neighborhood is basically the equivalent of a Cambodian middle to upper middle class suburb. It's about 5-10 minutes($1) on a motorbike to get to the riverside or street 51. I would guess the demographic breakdown of the area is probably about 90% Khmer and 10% NGO workers and teachers so it makes for a good environment where you aren't isolated from real local life, but you are not the only Westerner around either. You'll get hounded by tuktuk drivers and motodopes every few seconds right outside the market, but once you get 30 feet away it's like any other Phnom Penh neighborhood, you'll only hear "motobike?" about 3 times/minute
It's not for everybody, but I think as far as Phnom Penh goes, it's where I would want to live again.