The best young talent seems to be defenders with Diomande, Inacio, Antonio Silva, and Fresneda being very talented.
Attacking midfielder wise Pedro Goncalves is the best one. Amazing stats for Sporting and lots of talent, still only 24. 20 goals and 12 assists last season.
CM wise young Joao Neves from Benfica is the most promising. Moutinho is his favorite player and you can see why.
Pepe (winger) is a interesting player from Porto who can also play the wingback position effectively.
After the departure of Ramos new signing Viktor Gyokeres seems like the best youngish striker (25yo). Very powerful runner who is good technically and has a powerful shot. He has started the season well for Sporting but I won't vouch for yet until I see more of him.