Personally I prefer RegisterFly. It's an eNom reseller. Their prices are very good, especially for U.K. domains, and overall their support is great. What I do find is that ever since they introduced their live chat support, their support has declined in quality. I find that support from their helpdesk is very good though.
I had a concern one day, and contacted them. Their CEO replied to me, and I was very happy with the response. I probably won't change. RegisterFly have had some hiccups, but overall it's been great. The only problem is they cannot register names like .fr or .de or .be or things like that. When they can, they'll be the best available I think - If their service stays the same.