Since when does trusting a business critical function to a free service make any sense? At least GoDaddy has a motivation to provide some level of service because people are paying them.
I use the latter one and in addition to providing an alternative to my registrar, they also seem to have much faster response times, which cut some milliseconds off a site lookup.
My suggestion makes sense since they are a very big ISP and they simply don't care about the cost of a service that they would need to provide to their clients anyway.
Namecheap does the same and most people think that they provide a good service.
Seriously, pay if you want, but if you aren't Google, you don't need to pay for reliable DNS hosting.
Some other alternatives that aren't free, but are highly reliable are: http://dyn.com/ http://www.dnsmadeeasy.com
I use the latter one and in addition to providing an alternative to my registrar, they also seem to have much faster response times, which cut some milliseconds off a site lookup.