I shouldn't be reading this thread since I'm second guessing my upgrade decision and this thread isn't helping. 😉 I had both the 9.7" and 12.9" 1st gen iPads Pro, but have upgraded the 9.7" this year to the fully specked out 10.5" iPad Pro and I am also keeping my 1st gen 12.9" iPad Pro.
For the past year, the 12.9" has probably been my favourite size. The 9.7" was great and portable, so went in my handbag, but the 12.9" was the one that I mostly reached for at home. I love the 10.5" upgrade from the 9.7" and it's my new take everywhere iPad.....but it will be interesting to see which one I end up picking up more often in a few months time. I think that I'm feeling a little torn at the moment since I'd love to have the 512GB storage in my 12.9" and I wasn't happy when Apple released the 256GB 1st gen only some months after launch. I'm close to making my 12.9" my main computer, but feel that the storage is holding me back. I have 512GB now in my 10.5", so it will be interesting to see if that becomes my main computer, over the 12.9". My current thought is that I will upgrade the 12.9" next time to the maxed out 12.9" iPad Pro gen 3. One of the reasons that I upgraded the smaller Pro this time was because my husband would then get my 9.7" Pro and 11yo daughter would get the iPad Air 2 (upgrade from mini 2). My 15yo daughter has the iPad Air and is in line for the 12.9" Pro next time since she is very keen for it, while the others like the smaller size. So, the whole family upgrade plan played into my upgrade decision and I think that I made the right choice for that reason, but if that didn't come into play, I think that I would have upgraded the 12.9" this time around. I'm sure that iOS 11 will give my 12.9" a nice upgrade until the next hardware update....and then I will doubly enjoy the upgrade.