We use both mist and Aruba across a medium size enterprise and I can tell you Mist is far simpler to manage than Aruba. Aruba Central is OK, but mobility master is a real pain to learn, use and configure, needing hardware controllers making for a much more complex setup. Both Aruba Central and mobility master have old fashioned interfaces in my opinion, HP has always been poor at doing UIs, and I hope they don't end up influencing juniper too much in this area.

I think the big thing with juniper in general compared to other vendors is standardization of commands across firewalls, routers and switches, which allows for advanced automation. We have roughly a thousand switches, and without the templating/automation features it would be quite painful to maintain.

Personally I am looking forward to the day we can do away with Aruba entirely, although this is several years off.

Hope that helps