AdSense is traditionally the best. I've tested this against the Yahoo and Microsoft offerings as well as all of those annoying link injection ads by companies like Kontera and AdSense has always done the best.

However, for many people, like Jeff Atwood on Stack Overflow, AdSense is a failure. So depending on your topic it might not work.

I would sign up for an account with each and every advertiser that you can find and then run each one for a month and compare the results. It's the only way that you can know for sure.

If you don't like the idea of adverts then you could create an exclusive member's only area of your blog and charge subscription for it.

Also, you could have benefactors receive your blog posts 24 hours earlier than you post them.