Stay in all three quite regularly. MY order of desirability:
1. Reston
Distant 2nd. Fair Lakes
About the same 3rd. Dulles
Fair Lakes vs Dulles: There is nothing around Dulles, but there are two malls a very short walk from Fair Lakes, plus the Fairfax Corner (name??) a short drive. Fair Lakes is also slightly more convenient to downtown DC (take 66 east and no tolls). Both hotels are a bit tired, but food and staff and other facilities are fine, and similar, at both.
Between Dulles and Fair Lakes, if you're just needing a place to stay...go for the cheapest.