Just my input, if you don't have lots of packs (like 100+) then focus on skill level. If you train a 4* up to 5*, it's true he will lose the star in two weeks. But if you train SA, just means you have a 3* with SA in two weeks. Personally, that's not god enough for me. I try to buy in players who have multiple positions or SA so I don't have to train those