I would suggest you to go with Mochiads actually, NG Ads doesn't seem very stable right now.
If I compare the MochiBot stats with the NG stats for my game Cheat2Win for June, then only about 1/3 of the views actually generated an ad impression (and for a view to count you must proceed from the preloader, an impression can be generated by just loading the game).
On top of that, the eCPM for those impressions were as low as $0.002. This doesn't bother me so much as the game doesn't have very many views anymore, so even in the best case scenario I wouldn't make very much from it, but still. I have contacted PsychoGoldfish about these issues, but he never got back to me.
So to conclude: I haven't tried MochiAds myself, but if I had to choose an ad service today it would definitely be them, simply because NG ads seems like such a risk to me.