My experience
Goalkeepers penalty stopper - Useless
I've conceded 3 penalties in 6 seasons (and almost all teams have a penalty specialist) and never played penalty shoot outs.
One-on-one stopper - Almost useless
Every time an attacker is on-on-one with the gk, he doesn't shot on goal but gives an assist to another player, who scores.
Aerial defender - Very useful
Defensive walll - Useful
Totally quote dv8r
Playmaker - Useless
Few assists, few goals
Dribbler - Useless
Totally quote dv8r
Shadow striker - Slightly useful
I had a AML-AMC for 3 seasons, 7*, 6*, now 5*. He's good but he scores from long range from time to time. Not more then other good attackers.
Striker, One-on-one scorer - Slightly useful
quote dv8r
Penalty taker - Slightly useful
My players with this ability never missed a penalty, on the contrary of other good attackers. But I don't shot many penalities in a season
Free kick specialist - Very useful
They alwayes scores a lot of goals from free kicks
Corner specialist - Very useful
My DC-DR with this ability gets a lot of assist through the seasons