My current iPad Pro 10.5”. I’ve only had the iPad 4th Generation and original first iPad, so the competition isn’t exactly strong. As most Apple fans know, the first iPad did not last long at all, especially compared to the iPad 2, and the iPad 4th Gen did serve me well for a while, but get really slow after like 3-4 years. I’m on my third year with the 10.5” and have yet to see major slowdowns.
I’m sure my actual favorite would be a 2020 12.9” Pro, but I haven’t bought it since I still don’t consider it enough of an upgrade, which is a testament to how good my 10.5 has been.