if you buy only one scout make sure he is not older than 23-24 years and that he is topped with a good special. Free kick special ability and corner SA works pretty sweet the rest i am not sure about working at all.
When i talk about topped i mean a 24,29,34 or 39 player and so on.....!
I would only bought a scout for a key position like, Goalkeeper, DMC or AMC! This is if you can only buy 1!!!