Google is more popular and more used than adbrite. I am sure you could get cheaper with adbrite but more exposure with adwords.
If you use AdBrite for advertising, you just have to make sure that you carefully pick the sites you want to advertise on. Don't use their network ads, I don't think they are as effective. If you go to the AdBrite Directory, and sort by lowest CPC, you should be able to find some good deals. I have had times where I have done that, bought an ad for $3 a month, and ended up receiving 2k visitors a day from that ad! Talk about a deal! You just have to make sure to research the website your ad is going to be on. View the website, see if their traffic fits your niche, and check out where on their site your ad will be seen. Good luck!