Android : What are the best services for rewarding players after watching an advertisment

I want to give the players of my android/IOs app the possibility of watching advertisments to get ingame rewards.

Currently I use AdMob for displaying banners and I don't even know if you can get the confirmation if the user watched an advertisment. I read that it's agaisnt AdMobs TOS to reward the player for clicking an add but I couldn't find any confirmation on that.

I took a quick look and company names like AdColony and Flurry popped up. I'm wondering, what are the benefits of using any of those services over the other since I currently feel quite overwhelmed.