Either Coarse or Fine.

Coarse will sharpen a blade to a nice working edge relatively fast, but it's difficult to get a nice shaving sharp edge. Fine is slower, but allows for a razor blade like edge.

I like Coarse for modern hard blades steels (like S30V or D2) that are notoriously difficult to sharpen. If you're only using it to sharpen your Farmer, the Fine version would likely be better. As Victorinox steel is pretty easy to sharpen and does well with a nice fine edge.