Narvi

They all work and all have advantages and disadvantages. Sometimes I use a dremel-type tool with a mini drill press stand to make holes - this gives a dead straight stitch but looks kind of boring, like machine stitching. Also, on a large projects it can be tedious to mark and drill so many holes. On the plus side, it works great on multiple layers of leather. The diamond stitching chisels from Tandy are fast to use and look pretty good. But on thicker leather the holes are much bigger on the front side than on the back, so you get a decorative slanting stitch on the backside of the work but the stitches sit down in those deep holes on the front side and look straight. I don't use a stitch wheel because I've had too many problems getting consistent markings, but sometimes I use the stitching chisels like a pricking iron, just to mark the holes without going all the way through the leather. Then I use an awl to complete the holes. This give the prettiest stitch - a nice decorative slant that looks the same on both sides of the work. The downside is that using the awl lengthens the stitching time considerably, maybe by 50% or more vs using the stitching chisels to make holes all the way through the leather. If time is not an issue, this is the best way to go IMO.

Beautifully done detail from Michelangelo's Creation of Adam. Left hand looks kind of creepy on its own, though.