iPad Air or iPad storage

The best advice is to purchase as much on-device storage as you can afford - as iPad internal storage cannot be altered or updated.

Far better to have more device storage than you need - than to later discover that you need more storage than you have. You can never have, and we never see complains of having, too much storage - whereas you will see many tales of woe from those that sought false economy in choosing a device with storage inadequate for their needs. Having more storage than you perhaps anticipate provides room to grow as your needs mature.

A general computing “rule-of-thumb” is to think carefully and quantify your expected storage needs - add a healthy margin - then double it.

My recommendation - and that of many that participate within these User Communities - is to purchase as much internal storage as you budget will allow. Personally, I would suggest that 64GB is simply inadequate for the majority of users. 128GB or more is a much “safer” option.

I hope this information and guidance proves to be helpful in guiding your thoughts.

A 64 GBs iPad only has about 50 GBs of actual, usable internal data storage after internal storage formatting, installation of iPadOS, which is a fairly significant size, now, and a maintaining of 2-4 GBs of iOS/iPadOS operational reserve internal data storage space at all times.

64 GB is not really inadequate, ( 32 GBs devices are the really inadequate iOS/iPadOS devices ), and is a usable amount of storage space, but yoy may find yourself using up that 50 GBs of internal data storage quicker than you may anticipate.

Old stored data can always be backed up/archived to your MacBook an.or online, offsite data storage/back up services, like Google Drive/Photos, BOX, DropBox, etc..

The iPad Air 4 has nearly the same screen size as the 11 inch iPad Pro.

It is just only about 1/16 of an inch smaller, at 10.9 inch diagonal screen.

Also, the 2020 has a laminated screen and Apple Pencil 2 compatibility

Also, has true stereo speakers with 2 resonance chambers.

Also, iPad Air 4 has the latest internal processor ( A14 Bionic ) with 4 GBs of internal processing RAM.

In addition the iPad Air has a 7mp front facing camera and a 8mp rear/back camera

The 2020, 128 GBs 8th gen iPad has a smaller 10.2 ( nearly 10-1/4 inch screen that is nearly 3/4 of an inch smaller than the 2020, iPad Air 4 ), but this iPad has an updated internal processor that has been updated to the same processor that was used in the 2018 iPad Pro ( A12 Bionic ) but only has 3 GBs of internal processing RAM.

Also, the 8th iPad still has the pretty poor.pathetic 1.2mp front FaceTime video camera that Apple has been pushing into many of their iPad models since the 2012 iPad 3rd generation.

My over $1K 2015/2016 iPad Pro has this crummy, pathetic front facing, FaceTime video camera!

No laminated display. Original, 1st gen Apple Pencil support.

No true stereo speakers

You get affordable 128 GBs of internal storage ( actual, usable internal storage is qpprox. 110 GBs ), but you just have a basic iPad.

You need to weigh all if the added features, too, of the more premium iPad models, now.

Not just the storage size, alone.

The 2020 8th gen iPad WILL do everything the more feature rich 2020 iPad Air 4 will do, but it is more about user feature options, as well as internal data storage.

Best of Luck to You!

Just remember that whatever you get, it is stuck with that amount of storage. It cannot be upgraded. I am otherwise unfamiliar with the two models (I have an iPad 2).