This is market cap, but if you look at amount of traffic you have Akamai estimated at 15-30%, CF at 10%.
So if it would go down, it would cripple vast amount of internet.
Akamai is balls deep in video streaming, which is probably the most bandwidth/traffic intense thing for a CDN to dabble with. My guess is that CF has much more diverse traffic. Hence the fallout from an interruption would be quite different.
Fastly's free offering gives you "$50 worth of traffic" whereas Cloudflare has a perpetually free option. And for Akamai you have to apply for a free trial.