I would go with one of two strategies:
1) You want an iPad to use on the go, to have with you when travelling, and for texting, communicating, reading books etc. In that case, get the iPad mini 5.
2) You want to be very productive with your iPad, editing videos or pictures, writing large documents, taking notes in class with Notability on one half of splitscreen, and your text book pdf open on the other, you want to do music creation, notation, or use your iPad to store all your sheet music. For these usage cases, get the iPad Pro 12.9.
For the best of both worlds, one of each! 😁
I would love to see in iPad Pro mini, with the new design language, speakers on both ends, and apple pencil 2 support. This way I could do the buy both iPads and only need one generation of pencil for both.
To me, the 9.7 and 10.5 inch range options are too large to take around everywhere with you, and also are limited with productivity as they do not support two apps in splitscreen remaining in ipad mode. They switch to iphone mode on all ipads smaller than the 12.9.
Go small or go big, or go both!