I have worked with GOG, and you can''t go wrong there.
I purchased my stone from mark T. at engagementringsdirect...and his prices are awesome and he is super fast and he can get you whatever you need and give you an honest opinion. He also has a good return policy and 90% upgrade.... I am actually purchasing another smaller stone from him too! Reena and Alexah purchased from him. Check out there awesome stones!
What are you looking for? Many of the listed vendors are very good. At times it comes down to who has the stone in stock that best matches what you are looking for. If this is your first on-line purchase, I would recommend you stick to in-stock stones and avoid drop shipped stones.
All Blue Nile non Signature Series are dropped shipped and WF non ACA and expert are not in their possession. I don''t know if they bring them in before shipping though.