Number 1 (straight line lead-in with very short straight line lead-out) is desirable for any sharp corner.

Number 2 (arc lead-in with short arc lead-out) is good for thinner and softer materials.

Number 3 (straight line lead in with no lead-out) gives good results on thicker, harder material.

Number 4 is an example of a straight line lead in with short arc lead-out. CAM software should have the flexibility to combine different types of lead-ins and lead-outs should the user wish to experiment.