Namecheap.com is fantastic. I have been using them for about a year for a variety of commercial tasks and they have been extremely helpful, and they are inexpensive. You can get someone online to help you, as far as I can tell, 24x7. I have also used the certification service that they provide and they were also excellent.
I have also had many years of good luck with getting and managing domains and DNS through NearlyFreeSpeech, and while I have found the company to be completely reliable and easy to work with, they have two issues. First, they will help you via email, and if you send them some small amount of extra money they can be very fast about it, but there's no interactive help.
Second, NFS has a policy where only actual individual people can have accounts (not companies) and each individual person can only have one account. To do otherwise is a TOS violation and they really don't like it. Thus, if you're starting a company and want to manage the domain along with other people at your company, you basically can't. You can share control of a web site at NFS with other individuals, so that you can all get NFS accounts and work on the site, but you can't share control with domain management. I've told them this makes them unusable for enterprises and their response is, well, maybe so, and we might not be a perfect fit for everyone so oh, well.
That sent me to NameCheap a year ago on the recommendation of some other people I trust, and we have been able to set up a company account, name multiple contacts, and so forth. Very easy to do.
Your mileage may vary.
I inherited a domain about a year ago that was at GoDaddy. It seemed workable enough. GoDaddy is a marketing circus, though, so I didn't do much with it other than to make it point to my servers and log out. I don't know enough to recommend it or not.
Hope this helps!