Its difficult to say. There are ones that are easier to get a feel for because they are part of events that happen more often. Like corners & free kicks and their defensive equivalents (aerial defender and defensive wall being 2) - that might in itself be enough reason to get them.
I get a lot of goals from corners and free-kicks and those taking them have the SAs but they are also my best players. But a lot of goals come from dead balls anyway.
So I want Aerial Defender and Wall. If I got a winger or 2 with Shadow Striker I'd be pleased too.
SAs confuse me but I'd rather have them than not.