I would either use Godaddy.com or Name.com. Personally name.com because depending on the TLD you use, you get free private whois and it's cheaper and easier to use. But Godaddy is a bit more official and stuff. So yeah, hope this helps.
I think GoDaddy would be your best bet. It may be a little more expensive but GoDaddy seems to be very well known and used by many. I think I may just check into this myself!