I’ve had both. I honestly can’t remember which way I voted in here because it’s been a while, but I think the 11” is probably the better all around device. I currently have the 12.9 and wound up buying a mini because I just couldn’t get comfortable using the 12.9 with the MK anywhere other than a desk or table. I have used it in my lap occasionally with the keyboard, and although it’s doable, it’s not really comfortable.
That said, I think the 12.9 makes more sense for me because I use it as my only computing device. Since I type on it a good bit, and do other “computer” things with it, it makes sense for me to have the larger keyboard and screen.
For travel, I take the mini.