if you are serious about DNS
then you use a serious DNS provider, someone like UltraDNS, or Dynect. I've been a Dynect customer for many years. Neustar(owns UltraDNS) keeps trying to talk me into UltraDNS (I am a Neustar customer in other areas) but Dynect does the job, never seen an outage in almost 7 years (or *any* service degradation for that matter), they claim 100% uptime over 10+ years I think. 15 second SLA. Dynect gets DDoS'd a ton as well(they run an RSS feed with service updates), never seen an impact. UltraDNS has had some high profile outages due to DDoS..
Maybe cloudflare's stuff is ok(still too new of a service for me to consider), though it wouldn't drag me away from dynect. Cost is very reasonable, service is good, uptime for me has never been anything but 100% (I remember reading about CloudFlare's juniper issue a while back...)
Also if you're *really* serious about DNS then you'd use more than one provider.
Not affiliated with dynect in any way just a happy customer, and surprised to see some folks out there not take internet-facing authoritative DNS too seriously(like you can throw a couple of BIND systems out there and be done with it, or rely on something like godaddy). Now for hobbyist stuff that is fine(I host my own DNS for my ~2 dozen domains), but for the companies I work at(that make real $$), I want something *good* (if not the best).