Cloudflare have the fairest prices since they don't run their registrar to make a profit... but for the last 20 years I've been telling people not to get their domain name and their hosting from the same place so I'm conflicted...
Several reasons, some more relevant in the past or with smaller hosts, and aren't so relevant with Cloudflare:
* You miss a hosting bill and you provider takes your domain name hostage
* Your site becomes too popular and goes over "acceptable usage" and your account gets closed…