When purchasing check to make sure the steel plate is flat. Diamond stones cut well and last a long time. They are the best choice for honing carbide tools. No lubricant is necessary and surface resists build-up. Diamond stones are generally expensive.
Woodworkers have different needs when it comes to sharpening stones.
Try various stones and see what works best for you. Consider price, speed of cutting, quality or sharpness of edge, durability and usefulness.