My favorite OS on my cellular 64GB iPad 3 was/is 7.1.2, however, 9.3 is very close in usability for me. I performed a clean install of 9.2.1 and wasn't fond of my iPad on that OS so I put it in a box until yesterday. I did an OTA update, and am pretty happy with it so far with just email and light surfing so far. Surfing the web is a bit slow but it seems to be related to fetching of ads. I turned off most of my iCloud service synching as I don't need most of it (including Safari's data), but I do that on all of my Macs anyway - sync only what's necessary over the "cloud".
As a standalone device - no need to coordinate it with the rest of my ecosystem, I'd likely stay on 7.1.2. Since I need to coordinate a few services - email, Creative Cloud, MS Office - 9.3 is the nicest iOS version on this heavy beast, by a country mile. I own an Air 2 to compare it to, too...