My Two Cents
In my lineage we train San shou techniques with a partner to develop each technique...there are multiple techniques that can be used to stop a straight punch, an upper cut or hook...Basically you train the techniques, learn them, and which ever one your more comfortable with will flow naturally when you fight/spar!
But I suggest first try using each technique in sparring to see which one works for you. Everybody is built differently with different attributes. Use those that best suits you to your benefit. Personally i wouldnt use a fook sau to defend against an outside attack, Nor would I use a gan sau for an outside attack...I reserve the shorter techniques for inside fighting.
If someone throws a Jab i will use a fast pak or gum sao...If someone throws an upper cut Im not going to Low Bong Sao like some people suggest. I will use a low gum sao, low gan sao, or jut sao. For a hook or round punch I will use a Bil Gee, High bong or Wu sau what ever takes the most pressure off and cuts the punching arm force.
If your not sure about what techniques to use best..have a guy alot bigger than you throw medium power punches at you...an see which techniques hold up the best against various hits.
The Flow is relentless like a raging ocean with crashing waves devasting anything in its path.
"Kick Like Thunder, Strike Like Lighting, Fist Hard as Stones."
"Wing Chun flows around overwhelming force and finds openings with its constant flow of forward energy."
"Always Attack, Be Aggressive always Attack first, Be Relentless. Continue with out ceasing. Flow Like Water, Move like the wind, Attack Like Fire. Consume and overwhelm your Adversary until he is No More"