I never had any luck with Adbrite as compared to Adsense, but I do agree that placement is important no matter who you go with. Color matters too. I've done better with darker or more mild colors than wild or bright colors.
that totally depends upon you, if you think that your blog is getting a huge traffic, then using PPC ads is a good options, you can use services like adsense, adbrite, bitvertisers and more :)