Each service is performing differently in different regions. Amazon CloudFront can be better in the APAC region, while Akamai might be better in South of Europe and the Middle east.
Since this is a physical service that depends on the actual location of their PoP (Point of Presence) servers, you need to measure where most of your users are, and choose the better service for that region.
You can see such a comparison about the CDN performance in different regions here: http://media.amazonwebservices.com/FS_WP_AWS_CDN_CloudFront.pdf
The main difference between CloudFront and Akamai is the number of PoP servers. CloudFront is using Super PoP approach, which means much fewer (edge) locations (54 as of January 2016 - see complete list here), compared to the thousands that Akamai has around the world. This is why CloudFront costs less than Akamai.
Having more PoP was crucial in the early days of the Internet. But as the Internet is developing around the world the difference in performance is shrinking.
There are even benefits for "Super PoP" in terms of cache, as there is a better chance of finding an element in the cache if you have fewer cache servers.
If you are hosting your web servers in EC2, you will probably get better performance and surely better pricing from CloudFront. If not, you should check the performance and pricing between the various providers.
Note that you don't have to be exclusive, as many big content providers are using several CDN and not a single one.
