I have been using it since the first beta. Its far better than any other release after 8.0 (yes from a year ago) but nowhere near like 6.0 or 7.0. I dont think you should upgrade. I wanna break that tablet everytime I do something with it.
This last upgrade made my iPad usable again. 9.2.1 was really really slow and stuttering.it's better now. Of course it's not iOS 6 but I giant step forward. Try to remember that we own a 4 years old model..
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...
I don't have any good experience with iOS 9.3 on my iPad yet. Sadly, it's slower than I expected and got some other errors too. It took me 2 trials in order to get the firmware installed successfully. Seems like other people can't send images through their Messages.app either http://appletoolbox.com/2016/03/top-three-ios-9-3-problems-how-to-fix/