The OSB was cheaper, seemed lighter, and was available in the 5/8 size I was looking for. What I didn't discover until actually painting it was that the 2 sides of the OSB are textured differently. One side feels smother in most places but you can feel the bumps and dents. The other side has a checkerboard pattern to it and feels rather rough to the touch.
I assumed that the rougher feeling side was less of a finish side so I put it on the inside. After the patching, sanding and the primer; the cabinet outside needed to be done again to fix all the places I missed. The inside came out very nice and I only had 2 very small spaces I had to patch again.
Part of the idea of making this cab was to do it as cheaply as possible. If you notice in the first few photos, not all of the wood is OSB. I bought 1 sheet of OSB and the rest is all leftover wood from projects other people in my family were doing.
I sanded and put another coat of primer on last night. It looks MUCH better. I will try to post a pic tonight.