Which type of eye liner works better?

Depends on the effect you are after. Pencil is definitely more versatile as you can create wide or narrow, sharp or soft lines as well as being able to use it instead of an eyeshadow for a smoky-eye effect. Liquid liners, although more difficult to apply accurately, will give sleek cats-eye definition but there is less variety when it comes to the effects that can be created. I would personally opt for a pencil but build up the definition with a liquid liner for a more pronounced effect.