For me, the 11 inch works great. As I posted pages and pages ago, when I first with to the Apple Store on launch day, I looked at both and was sorely tempted by the 12.9. There's something about how they've got it displayed that makes it look just right. But I had settled on the 11 inch previously, and now that I've got it home, I agree that it's just what I needed. I'm a shorter woman with small hands. Plus, I've got a 13 MBP; I felt that the 12.9 iPP would be redundant.
This is my first iPad Pro, though I've had an Ipad since they came out. I found the 11 IPP (once I was outside of the Apple store) to be surprisingly large, especially compared to the 9.7 that I'm used to.
I strongly considered the regular iPad. In fact, I still have 8 days to decide. But I use my iPad a lot, and I wanted to at least try the Pro product with Pencil and ASK. I have a collection of iPad keyboards, none of which I've liked, but I really like the ASK, and unfortunately, it only works with the Pro.