We used akamai for a year, then they kicked us off for being an adult business (we weren't even hosting adult content on their CDN, but since they have CDN delivery locations at places like public schools, they decided it was a PR nightmare waiting to happen).
Then we used Speedera for a year or two; they were great. Then they got bought by Akamai, and a couple of months later, Akamai kicked us off.
Now we're using
Limelight, which is both cheaper and higher performing than Speedera was (according to our international QOS measurements). I highly reccommend them. Just request some kind of refund clause in the event they, too, get bought by Akamai.
Cheers
-b