Reply by bilyo

I will second what jkm312 said. Let me emphasize what he said about the right size hole; particularly when using plywood. Remember that your dowels are like pistons. Particularly when glue is applied, clamping the joint closed can put a tremendous amount of pressure on the sides of the hole and can easily de-laminate the plies. Make sure your dowels have grooves to allow excess glue to escape and make your holes slightly deeper than the dowel by perhaps 1/8”.

IMO, splines in plywood are easier and less apt to cause problems but there is nothing wrong with dowels.