I cannot understand why this plug-in is not better known. I found it yesterday (after running my self-hosted site with AdSense for a year) and added it.
It is already generating income for me, and over the course of a year the additional sum is going to be noticeable - possibly an extra 10% on top of my existing AdSense income.
A 320 x 50 ad unit does seem to be the best option, it tucks in nicely between the post and the sharing buttons. Looks fine on an iPhone 5, have yet to try it on a device with a bigger screen.