After about 2 weeks of testing, I have some more information that will help.
Even though the InMobi support is better than that of MobFox (at least for the past 45 days or so that I am using both of them), if looks like MobFox is performing much better than InMobi. InMobi promised to provide $0.6 CPM for specific (high paying) locations. I have tried that for 1 week and the average CPM they delivered was around $0.24 (not even half what they promised). After complaining, they said that they cannot give me what they promised but they will work on it.
I think this is b***t. If you cannot guarantee a given CPM, do not promise it. I guess that most (all but AdMob) ad networks do this. They promise high CPMs but I doubt that anyone can get even close to what they promise (this is as far as banner ads are concerned since this is what I am using).
If anyone knows a company that can keep their promised CPMs (for banner ads), please post it here. I have also started using Flurry but still, AdMob is by far the best.