Super Vision will help you react to plays quicker, and not get faked by elusive backs.
Closing speed will help you catch the ball carrier for more tackles and more chances to FF.
Wrap up tackle boosts your tackling score and might help with FF's... but it might be a flat bonus which means not too helpful.
Head hunter is untested as far as i know but might help with the FF's.
Change Direction will help you make cuts better to keep up with high AGI ball carriers.
First Step will boost your acceleration so you can get to plays faster.
Gang Tackle will boost your tacklign score if you play in the middle a lot... might be a flat bonus which also means not too helpful.
Diving tackle gets mixed reviews, some say it helps and adds range to DT's, some say no effect.
Jack Hammer will help if you are used to cover the TE a lot and are a hard hitter.
There are a lot of bonus SA's ,and without knwoing your build plan there are quite a few directions you could go.
If you aren't absolutely certain of your build direction, hold off on switching out your bonus SA until later, the more times you switch your bonus SA the more BT's it costs... so don't switch until you are absolutely sure what kind of role you want to play.