Cheap but horrid when you need something
GoDaddy is the most popular, in the same way McDonalds is. It's cheap. Good for when you need a personal website with a blog read by about 5 people in the world.
But when you need serious websites, they suck big time. The customer service is the rudest I have ever encountered (what's the "service" for?). The web interface is pathetic and cumbersome requiring about 10 clicks for every single thing. If you wish to simply buy a new domain, it will take you through about 7 screens of cross-selling and whatnot. Stupid, stupid experience.
Most importantly, their anti-abuse policy is now crap. Pure drivel. People's websites can be "spamvertised", which means I don't send spam, but my websites are now so busy and popular that spammers phish my domain name. GoDaddy is not for sites like these with huge traffic. They do NOT know how to cope or manage with technical savvy.
For small homemade domains, GoDaddy is fine. If you are planning on run serious websites, forget them and look at Tucows or eNom. You get what you pay for. With eNom, you can try "bulkregister.com" if you wish not to pay for their reseller services.