Totally a preference thing. My wife’s 11” iPadAir is great for her, my 12.9” iPadPro is great for me. The 12.9” is too big/heavy for her, the 11” is too small for me. Try borrowing one of each and decide which you like better.
This. I find the 12.9” is just about useable for me, bordering on too big and heavy. But it totally depends on your arms and where you sit, if you’re a large and muscular person you may find it perfect.