If you are tall, the tall one. If you are of standard height, the standard one
In reality it depends not just on overall height but body length, seat height, typical riding position etc I.e. how high your eyes are. As a very rough rule of thumb maybe if you are 6 foot plus then start to consider the tall one, but the only safe way is to try it. Nowt worse than looking through the top of a screen... An adjustable bracket like a Madstat gives you huge flexibility here.
If I get round to it today I'll measure the height of my (tall) MRA above the tank...