every player in my team has SA apart of my DMC because of rubbish selection (no defensive walls unless you have DC/DMC which I dont have)

usefull ones

corner taker - I have 2-3 players with this special ability and its very important especially in Cup games
Free Kick taker - I have 3 as well in case I am playing 2 games a day which I usually do.

Defensive wall - is the best one for blocking the shots, I have 5 defenders and they all have it - very important as I do concede 10 goals per season in League in average, no more

Shadow Striker - yes but only for AML, AMR based players ... sometimes when I have ST, AMC I give it to him

The rest are pure rubbish, the top one is Penalty taker and he cant take penalty properly, plus both GK abilities are rubbish plus the worse one is definitely Playmakaer which attracts lots of cards and its useless.

It costs 50 points I know (it can be trained within 10 hours if you have Nordeus gen player)

The best thing is when you put this kind of player into tranfer market (first 2-3 days) bidding war goes for around 25 rounds easily, I love it Sometimes to watch this bidding wars is much better than to watch some Yankee movie , trust me