The "AVOID TERRAIN" and the "PULL UP" alerts are straightforward: pull up for your life.
"SINK RATE" and "DON'T SINK" are straightforward, too: correct it if you don't want to get in trouble.
"TOO LOW GEAR" and "TOO LOW FLAPS" are straightforward as well: go around
"GLIDE SLOPE" is straighforward, too: correct, or ignore if intentional
"TERRAIN AHEAD" is relatively simple. Adjust flight path by stopping descent, starting a climb and/or turning as necessary to avoid terrain as shown on the ND.
But the ones that seems ambiguous to me are "TERRAIN-TERRAIN" (excessive terrain closure rate) and "TOO LOW TERRAIN" (unsafe terrain clearance when not in landing configuration) :
Adjust the flight path, or initiate go around
May I choose? Based on what?
A After “TERRAIN” has sounded twice, the warning switches to “PULL UP”, and is continually repeated until the aircraft leaves the warning envelope. In addition, the PULL UP lights come on.
It sounds quite serious to me. If I am in IMC or in a dark night, I'll go around unless there is specific information of that airport giving false alerts.
A "TOO LOW TERRAIN" alert comes if you are flying at 250 kt or more and below 1,000 RA without being configured for landing (that's not good). If you are flying at 170 or so, it will come at about 300 RA and not configured yet (that's bad)
It is a very serious one, which I will regard as genuine unless I can see with my own eyes.
I totally agree with Safetypee. If I disregard a GPWS is because I can see terrain with my own eyes or if there is reports of nuisance alerts. I will never disregard a GPWS alert in IMC or night because I am convinced I have been doing everything OK so far and there is no reason for an alert.