Chains and pinions are okay so long as you give them enough teeth. If you go for low tooth count sprockets to get low speeds then cogging becomes an issue. A 6 tooth sprocket is much the same as a hexagonal pulley wheel.

Pinions tend to have awkward tooth forms in the smaller tooth counts to engage the rack which can lead to minor cogging and you also have the problem of keeeping the pinion engaged. Someone was making racks with a vee back which looked interesting, might have been Hurco.

Good points with sprocket and chain are:- Low price. If both ends cog in phase you can apply massive spring tension without adding to the rolling resistance or having to worry about stretch. Real easy to connect to the driven item, all you need are a couple of holes.