I've had fun and games with various different web hosts over the years and service levels ranging from restrictive to blatantly annoying. The jokers who lost a full months worth of blog posts and IMAP emails because the "...hard disk has failed" were a particular set of idiots I'd rather forget (I mean, 'The' hard disk? Seriously?). However they're not all bad and in recent times I've settled quite happily with 123-Reg, for many reasons but predominantly due to their clean and simple options for self DNS management at NS (nameserver) level.
If you manage web hosting it's important to be able to point your domains NS records at nameserver names & associated IPs you manage, and create the relevant entries for doing so. Not all domain reg hosting companies will let you do this and of the ones that do I've yet to discover any who offer such an accommodating no-nonsense method of doing so than 123-Reg.
123-Reg provide a superb DNS overview which explains everything you need to know through A records to CNAME and mailserver (MX) entries in easy to understand stages. Download the free PDF HERE.