I would assume Prolexic or Incapsula, assuming they're using a high end provider (which they should, DDOS attacks against smaller DNS providers being so easy to carry out).

Hopefully not. CloudFlare is remarkably unreliable for a service that claims to improve uptime.

Curious to hear more about this.

+1 never had any problems so far.

[citation needed]

Last I checked CloudFlare routinely handles[1] 10Gbps to 65Gbps attacks, and has successfully handled attacks as large as 300Gbps and 400Gbps. According to this report DNSSimple crumbled under 25Gbps.

[1]: https://support.cloudflare.com/hc/en-us/articles/200170216-H...

Their last significant outage was only 2 months ago: https://blog.cloudflare.com/route-leak-incident-on-october-2...

As the blog post outlines, the outage was related to an upstream network provider leaking routes. Note exactly something we can prevent for them.

We moved off of CloudFlare because of repeated outages and bugs. Our uptime improved significantly without CloudFlare.

Granted we are probably more vulnerable to DoS, but our general uptime is far better now.