Machining offers some great features to it when choosing a manufacturing method. This method involves the removal of material. This means that the 'start' of your product would consist of a block of material. A couple common materials for this technology are stainless steel, and wood. Particularly with CNC cutting, a variety of pieces can be made from these 'blocks' of material. Essentially, a drill will come down and it will carve, remove material, and cut pieces of material off. Other parts within machining exist as well to remove material. This is great for making small quantities of product. It doesn't offer the variety, or the design capabilities of 3d printing, but it can surpass mold manufacturing in a variety of situations.
Mold manufacturing isn't like machining or 3D printing, as it involves molten plastic being shot within a mold, to harden and be finished. These pieces are very much cheaper to manufacture, and they can be manufactured on a much larger scale. Creating 1,000 action figures is much easier to do through mold manufacturing than the other methods.
3D printing stands out as its own kind of manufacturing. This process doesn't involve material removal, but the opposite. For this process to work, material is 'stacked' up on top of a build area to build up a final product. 3D printing uses a variety of materials, in fact over 100 exist today. Incredibly intricate pieces can be made with very organic curves, hollow spaces, and functional parts. Feats such as a ball within a ball have been made through 3D printing. 3D printing simply stands out for having the 'best' design rules to follow. 3D printing is very efficient in creating detailed custom parts on the small scale, but it can't very large products like machining can, and it is more expensive in some situations.
Overall, the style of manufacturing that you're looking at using depends entirely on what your product will consist of. If you plan to make 1,000 products to be sold to the masses, mold manufacturing is probably your best bet. If you need to design only a few, or a dozen parts that may be large, but don't have to be incredibly intricate, machining might be your best bet. 3D printing will likely stand out on all small scale orders that demand very precise dimensions and designs.