For me reading is the most important skill to improve.
You see, my goal is to be able to join any multiplayer lobby and first try 95% any map that is thrown at me. And for that I need to be able to read both slow AR and fast AR maps without any issue.
Of course, if you don't have an ego like mine that is hurt everytime I have to retry a map more than 10 times just to beat it above 98% (not 95% because if my goal is always higher then when I am playing multiplayer I should be able to consistently get accuracy above 95%) and you are willing to have maps with more than 100 retries then I don't think you need to be able to read at a high level, because reading only helps you beat maps with less retries.
My definition of reading: The skill that prevents you from hitting circles too early or too late in a succession. For example if you needed to hit circles which are in a square shape then bad reading should result in either too fast hitting of the circles or too slow hitting of the circles.