Mediavine is good but they want to get all available ad slots on the site. They will do the placement. They are really good if you have traffic from 1st tier country. They rejected my site with 1 million page views because my majority of viewers were from India.
There are a few recent discussions that could be helpful in evaluating AdSense alternatives - it is a question that comes up every so often. These are from the past few months: [webmasterworld.com...] [webmasterworld.com...]
In my experience, nobody pays as well (and as reliably) as AdSense.
If you start up with Media.net, you need to give them a few weeks before they start performing well for you. Supposedly they need that time to "optimize" - I don't know what all that entails. It's also true if you take your ads off for a while and then put them back on - get them to "optimize" them for you again and they should start performing better in a few weeks. That said - they didn't do near as well for me this year as they have in years past.
Facebook Audience Network was pretty good the first year (last year) and then they really tanked. I suspect they were getting lots of click fraud and tightened things up. Then they booted most of us out as we were supposedly "beta" publishers and now you can only get in by invitation. Unless you have an app, they're happy to do app ads.
SOVRN didn't do very well with me, and Vertoz ripped me off for a couple thousand bucks. The native ads in the Disqus comment system pay fairly well, but they pay out net 90, and they don't aggregate earnings if you have multiple sites (although I'm working with them on changing that last one)
On a brighter note, this year I sold more direct ads than ever before. Love me some direct ads!