After all of that is done, you have to decide where are you going to take him, Coverage or Hard Hitter.
This is my 2 cents and people can explain why they are effective, I will just tell you what is Top 3.
Coverage:
1) Superior Vision - Hard to argue against this SA that has big payoffs, but need to have like 60+ vision.
2) Change Direction - Could be #3 but speed/agility are PRIME for SS.
3) Closing Speed - Correct me if I am wrong but really only useful when playing either Nickel or Zone.
Hard Hitter:
1) Monster Hit - Only effective with High Tackling and High Strength
2) Big Hit - Less then Monster Hit, but allows for FF's to occur.
3) Superior Vision - Yes it is under coverage, but is effective for pretty much ANY position, but works with 60+ Vision.