I used to use 1&1 to deal with all my domains, but found they had a problem last year which took them way too long to fix. I moved them all to 123Reg and find they are pretty well organised, and I still use them.
I have used Godaddy lately, because I was working on something which was to be hosted in the US, and found their support department very eager to help with some not-normal technical issues.
At the end of the day, if it's just for Domain registration, use any one of the big names, and just ensure you go for decent hosting - it's way more important.