If you're going to use it for media consumption and be holding it a lot, stick with the 11". I had a brief foray into 12.9" for the first gen and went back to 10.5". 12.9 isn't really a good one hand device.
I have an original 12.5 and you really don’t realize just how huge it is until you lug it around all the time. I got a 10.5 for every day use out and around town. It is really a lot more discreet in the end. But the screen size of the 12.5 meant that I kept it also.
Got a 12.9 but I went to pick up a keyboard folio in store and saw the 11” it looked too small imo. With the 12.9” being smaller it seems the be the perfect tablet size now