The best for me! Accept Moneybookers and helpful customer service!
I started to register names with RegisterFly on 2005-07-21. And now I am getting to really like them. By now I am holding over 20 domains with them (and keep transferring all my domains to them). Their customer service helped me many times, especially with transfers of *.info names. Since I've tested them, now I am sure they will try hard to solve all my problems.
One of the most important features they have is Moneybookers payment option. It's very useful for me and it's free! Exactly. I make a local transfer (free in my bank) to load the money and then I can pay instantly on RegisterFly (which is also completely free) anytime I want. Fast, secure and free!
And what I love are their promotions. Anytime you want to register a new name or transfer one, they will have a great specials, $5.89 transfers, $7.99 registrations and renewals.
Something which is also worth noticing, they have Whois data protection free (if you read their e-mails carefully). What else? Now I am going to by some SSL certificates which starting at $15.99 which is simply great!
In daily use, very nice option is restoring the shopping cart. Imagine you put some names into, and then something happened to your browser. But you can click twice and get the whole cart back (actually you can restore a lot of previous carts from different dates!). They also had a great idea to create a Domain Tree - a tool to sort and manage all your domains easily.
Their profiles (for whois data and DNS) are very useful.
I cannot say anything about their hosting since I have my own hosting company.
In the end, I have to say that I really like them and by now there is no reason to even think about any other registrar.