The Slot Choice is meant to be a play that lets the Slot WR get open, no matter what the defense does. The Choice route will either get to its mark and turn around for a stop in place, or it will jet out to the outside, or cut in to the inside.
If the defender is playing inside, then the WR should jet to the outside. If the defender is playing outside, then the WR should jet to the inside. If the defense is playing in a zone, and is giving the WR some space, then the WR should just settle down and wait for the ball.
The Quarterback needs to have great chemistry with the WR so that they are on the same wavelength and can be expecting each other to make the same read.