Both solutions can scale as much as you want, you just have to make sure whether your budget allows it.
Akamai is the oldest CDN, with the most number of servers. The number of their networks exceeded 1700. It is a trusted solution that covers both the fastest delivery and the best security features.
AWS CloudFront has more than 225 points of presence, delivering the content pretty fast as well but it is slower than Akamai. Their security lags behind as well so it is better to use the security services of Amazon Web Services to enhance the protection.
The difference between server availability of both CDNs is insignificant and equals almost 100%.