IMO, the best attached keyboard option is Apple Smart Keyboard Cover. I have that and a smartcover for my 9th gen. Nothing beats the ASKC for portability and convenience. It is the thinnest keyboard cover/case option available for the 9th gen. I love the way it feels and it is my favorite keyboard for any device.
When I want to use the iPad as a tablet, it's easy to detach the ASKC.
When I want something a little more conventional on my desk, I'll prop the ipad on a stand and use the Logitech K380 bluetooth keyboard with it instead.