Choose only 1, or take time reading the rules and guidelines of each ad service, (don't worry I use adbrite and adsense on my site)
I use adbrite and adsense on different pages. I use adsense on the main page of my proxy and then adbrite on the proxified pages. I have been doing that for several months and haven't had any complaints.
As long as you can keep distinction between the two, both are good to be used together. In other words, keep your ad formats and ad colors different.
You might want to chime into a thread that was started at google groups about this a few weeks ago. Adsense Policy Question about Adbrite I have seen it done like others mentioned.. but like some said.. it can be tricky. Hope this helps
Yes I agree with him & so far i know that google adsense change the previous rules that was 'you cant place others contextual ads into same page where adsense ads are
Google also made it clear, you can use other ad network alongside as long as their is difference between the two ads.