I'm curious if you have upgraded your iPad? With only 16GB, I definitely would have upgraded -- I went from an iPad Air to the new iPad (5th gen) mostly because I was out of space with 32GB.
I agree with Just_Me_D, buy the size that you feel works best. I'm old enough that I appreciate the 9.7" iPad but, especially for those that constantly carry their iPad, I can see the appeal of a smaller iPad. It seems like, with current prices, there is no real cost advantage to not getting the size you want, at least between the new iPad and the Mini. At the same time, if you feel like you would use the Pro Keyboard or the Apple Pencil, you might want to consider buying the iPad Pro.
So, it depends on what you want/need -- though my one suggestion would be to buy at least 128GB of storage.