There are hundreds upon hundreds of sites where you can check availability of your desired domain name and purchase. In reality, though, there are only a handfull of domain registrars. Those hundreds of websites selling domain names are resellers. While you may find some amazing deals - usually for the first year or two - in the long term it makes sense to go with a company that provides good support. One of those is GoDaddy. If ever there is a need to request help with something, they are easy to get a hold of and generally very helpful.