Last year i had this dilema as well. Coming from 1st gen 12.9” i ended getting the 11” 2018 for the portability.
One year later.. still loving the decision. No regret.
I love how portable the 11” is. I can carry it anywhere and fits on most tiny cafe tables and economy class plane tray
Mind you i dont use split screen much but i do use slide-over alot and the 11” is sufficient for that.
I do draw, image editing, illustration, layout editing, 3d mockups and i dont find 11” too small, in fact it still amazed me what i can do on this little lightweight machine. The size makes everything fun.
out of topic but ipad 11 pro completely makes my macbook pro 2018 95% collecting dust i ended up selling it.
My suggestion is if you always almost gonna use the ipad on the table, the 12.9 is great for the larger screen. But if you want to carry your ipad everywhere like i do and use it one hand like a tablet, pick the 11” for sure
I think its a more versatile size.
Oh also if you do a lot of typing on the 11”, do get the smart / external keyboard because the on-screen keyboard blocks like 50% of the screen when on landscape... ?