I quite like Namecheap and usually buy all my domains through them. You get free whois protection and the prices are not too bad. They occasionally run promotions form really cheap (98 cent i think) domains.
I agree with Fowler when it comes to Namecheap. Their service is really user-friendly and their support is excellent. I register all my new domains with them and wouldn't use anyone else for that. Most of my GoDaddy domains have also been transferred to Namecheap.
I like how Namecheap operates as a responsible company and I like the free WHOIS privacy offered. However, I dislike the records management offered- once you transfer your nameservers its up to you to sort out mx records etc. on the other end.
I used godaddy for years but grew tired of all the in-your-face offers they have when you do anything on their site. I switched over to namecheap to save a couple bucks on renewal fee's and I was pleasantly surprised at the minimalist interface that is simple straight to the point. So in conclusion, namecheap is cheaper and easier to use.
I really like Namecheap the most personally. Godaddy tries to get you to check out other offers which can get annoying especially when you are trying to check your account. >_> Namecheap is also affordable and the control panel for the domain name is very easy to navigate.