The owner of SimpleCDN struck me as a bit flaky and rude. When I searched then for reviews of SimpleCDN you'll see some red flags in the way he responds to other people.<p>I asked something about this myself a long while back:
<a href="http://news.ycombinator.com/item?id=181010" rel="nofollow">http://news.ycombinator.com/item?id=181010</a><p>If you have your "showdead" flag on settings, you'll see some comments there that are kind of anti-SimpleCDN from people who had commented on nothing else before and/or just signed-up that day to comment. I'm not sure whether that's someone trying to discredit them or just a coincidence.<p>We considered using them (and played with their service a tad), but Cloudfront has been working well enough for our needs (since we also use S3 a lot).
One advantage that SimpleCDN has over Cloudfront is that it support http pseudo-streaming of flv and h264 video. I wrote some notes on it here:<p><a href="http://www.brightyellowcow.com/blog/Video-Streaming-Be-your-own-YouTube.html" rel="nofollow">http://www.brightyellowcow.com/blog/Video-Streaming-Be-your-...</a>
We've used CacheFly and have been really happy. The price is right and at our low number of transfers it always maxes out the customers downstream pipe. The only issue we've had is some of our customer's internal firewalls have blocked one of our files that 5GB+ but I guess that would happen not matter which CDN we used.