I have been through all form factors of iPad and enjoyed them all.
I initially used the original iPad form factor because there was no other alternative, obviously. But I've had nearly every generation of iPad since the original ... and I enjoyed even the 1st generation. I would basically carry it with me wherever I went as a better browsing/surfing alternative to my phone.
I switched to the Mini instantly because I used to carry around the bigger iPad's and found the Mini did everything I wanted (a larger screen web browsing experience, mostly) in a jacket or handheld form factor. I even gave up the retina screen for the original Mini ... thank god they eventually went retina on that. Those were exciting times.
When the iPad Pro 12.9 came out, I bought it to experiment with, but I still had the Mini. I found the 12.9 to be nicer around the house in very specific ways ... as sort of a "casual laptop" as opposed to the Mini. The iPad Pro 12.9 was frankly a terrible tablet for me ... too unwieldy and really only useful with the keyboard. But if you were going to be using it in that form factor sitting on the couch or in bed (or in a coffee shop), the larger screen and ability to type was obviously better.
With bigger phones eventually being a thing and the Mini appearing abandoned and feeling sluggish, I found myself not carrying the Mini around anymore in addition to my phone. So I sold it off.
That left me with the Pro. Good around the house, and for day trips in a coffee shop or waiting for the wife to run errands.
What eventually killed the iPad Pro 12.9 for me was that I got a Nintendo Switch. It turns out for the time being, I vastly prefer playing video games to surfing the web during my downtime, so that mostly killed off my usage of the iPad around the house or on small trips. Partly as a consequence of the Switch, I also adapted my usage at home so that I mostly just spend my time at my desk if I intend to web surf ... so there was no more lounging around on the couch or in bed. So no use for the iPad in those contexts.
I also found it increasingly ridiculous to have to carry around a Macbook for work, the iPad Pro, a Switch and a phone on trips. The Macbook was not optional, so the iPad Pro had to go.
The 2018 iPad Pro has dropped enough in price that I'm getting ready to experiment again with the 11". I've actually always preferred the iPad form factor as opposed to the Macbook, and my hope is that someday I can carry around an iPad Pro, a Switch, and a phone instead.
With reports of ARM-based Macbook's growing increasingly credible, there's really no reason an iPad wouldn't be able to run macOS, just like the Microsoft Surface line of tablets. That could make the iPad a viable work replacement for me. I mostly carry the notebook for responding to issues, not for serious extended work (that happens at a workstation with big monitors), so the form factor can be more to my preference (aka 12.9 vs 11 is not that important), but the ability to run desktop class apps and frameworks is not optional.
