For me the most important thing is the age of the draftee. I will try and put 18 year olds at the top of my draft list. Your ranking depends on what you want to achieve.
If you want to sell the player, then try and get an 18 year old with high potential and decent skills.
So if I wanted to sell I would pick a 3 star skills and 5 star potential over a 4 star skills and 4 star potential.
If you want to train up a player, then you should be happy with 4 stars in potential (or even 3 stars in potential if you don't plan on training him for many seasons). If you plan on training him for a long time then naturally potential is more important than initial skills.
This is a personal preference, but if any of my draftees have 2 balls or less in skills then I put them at the bottom of the draft list. Also, if any of my draftees have 3 balls or less in potential then I put them at the bottom of the draft list (unless it is a 5 star skilled, 3 star potential 18 year old which I would rank highly but would probably sell for a decent price.
Also I would only take a 19 year old if they had 5 star in skills and 4 or 5 stars in potential.