The Force Awakens, for me, had a fantastic mix of the feel of the original trilogy in the animatronics/puppet kind of look as well as just the right amount of cgi to make it still feel authentic but look like a high quality, sci-fi epic. So I have to say I think that edges out all the others for me.
In terms of pure storyline I still think that ESB/RoTJ are the winners for me though, I just love the Luke/Vader arc throughout that, but we'll see where the rest of the new trilogy takes us!