WadeL covered most of it. The bit I would add on POF is below.
What separates POF from the rest of the field is whether the community polices itself.
Two of us compared notes on the app and landed in the same place on how aggressively it pushes credits at you.
If you care about whether the active count matches the claimed count, that alone should decide whether the service is worth it.
Whatever you land on, test POF for a week before you judge it.