Joyce asked: “What is the best iPad to buy?”
Joyce, “best” depends on your needs.
The most advanced model right now is the 9.7” iPad Pro, it has all of the features of the 12.9” Pro, but with a 4K-capable camera, and better colors.
Obviously, if you plan to work with it and need a bigger screen, the 12.9” would probably be a better fit for you.
If you don’t want features like Pencil but don’t want an 8” screen, maybe the less expensive 9.7” Air 2 would fit your needs.
If you want to carry it around either of the current Mini models would be good for you. If you care more about saving money than you you care about a fingerprint sensor, the current base model, the Mini 2, would probably be enough for you.
The Pros can be adequate content production devices, the other models are better being used as media consumption devices.
The different iPads fit different needs so the best iPad to buy probably depends on what you want out of yours.