There are alternatives to AdSense, but the key here is to recognize that AdSense enjoys its favorable position in part by sourcing advertiser demand from other platforms. There is a massive and creative ecosystem around developing technology to suit (and sometimes to drive) the mercurial wishes of ad agencies. So Google captures this through partnerships. Ad demand that's actually originated by Google sales is very significant and very high quality, but there's no doubt that Google is simultaneously interested in serving its own wholly owned properties.
The best thing to do is to build relationships with 5-9 high quality ad platforms and waterfall them through passback tags, one to the other.
Good platforms include, but are certainly not limited to:
AOL
x+1
AppNexus
Turn
MediaMath
AudienceScience
Criteo
The Trade Desk
If you're lucky, you can satisfy all requests without sending a single impression over to AdSense.
If your domain is delivering fewer than 100m impressions monthly, it's unlikely that the companies noted above will be keen to put personnel on your account, and may not be able to work with you at all.
However, with intelligent switching, keen arbitrage, and an aggressive performant waterfall (e.g., you never actually want to pass a request to more than two or three of these or you'll see packet loss that exceeds the positive delta you'd have obtained by accessing yet another ad platform) you can do very well without using AdSense. The company I mentioned below, Publir, was cofounded by me about five years ago and does what we think is a rather good job of this. Sites like The Atlantic and others use us for their ads.
We're also terrific fans of BuySellAds, whose self-serve platform is second to none. There, your goal is simply to do direct outreach to advertisers likely to covet your audience. Even the finest brand-name publishers only sell about 30% of their ads this way, though, so your expectations ought not be too high.