I would consider anything 30" and taller a "tall" tank.
I LOVE tall tanks, and I think they look great! But, as others have stated, it is difficult for most to reach the bottom section of glass for cleaning and more difficult to reach/place corals without the need for the step stool. I've always got my hands in the tank, so shallow tanks are my preference, and I'm 6'3".
In terms of stand height...I used to build my tank stands high as others have said, so that I could look into them comfortably when standing. However, as I've gotten older, I find that I much more enjoy my time spent in front of the tank while sitting, slightly reclined with the feet up, listening to my favorite music, reading or perusing the internet with my laptop. A nice drink on the table next to me!
My next tank build will be a shallow reef, 18" to 20" tall with a stand around 30" tall.