Re: What's more comfortable - top or bottom bars?
 

Dynamic bars are the best, but not made yet (?). Simply make a gesture, and a bar will pop up close to your fingers. Then, it does not matter which side it is on, because it is on ALL sides!

Re: What's more comfortable - top or bottom bars?
 

Except for text entry, which pretty much needs to be horizontal, I prefer side bars on the tablet, because the tablet's screen has a lot more width than height.

That being said, I wish all of the bars and widgets would just go away when I'm not using them.