I like the Youths although I lately have been getting useless three stars. I keep a full squad, so mostly I release even the freebies. On one of my alts, I have kept a freebie, and he is my main wingback for his position... even though he is two star he does perform pretty good ratings, sevens and even an eight now and then.

But! On my main team I have bought quite a few of the four stars, and they do quite well usually.. and their market value is usually over what you would pay for $ so if you sell them you're not badly off $ wise.