The short answer is that the best knife to use for whittling depends on what you're whittling and why. If you're looking to carve simple shapes and figures, a pocket knife with a sharp point will work well. You can also use a paring knife—make sure it's sharp and able to be held comfortably in your hand for long periods. If you're looking to do more complex carving, then a paring knife is probably going to be your best bet. These are designed for more intricate work, so they have small blades that allow you to control where exactly the blade goes when you're carving. They come in both fixed-blade and folding varieties. Finally, if you want to do some of the most intricate carving possible, then a multi-tool with a small pointed blade is your best bet. These allow you complete control over what the tool does, but they also take some getting used to before they can be wielded effectively while whittling.