First, a correction of a misconception. You don't stretch ligaments. Ligaments connect bone to bone, and if they stretch out, they don't go back to their original shape. This makes joints loose and easily dislocated. (Very common in repeat shoulder dislocations). You stretch muscles.
Stretching before exercise - Studies have shown that static (reach and hold) stretching is contraindicated before exercise, especially in power based sports. So, if you do anything before exercise, dynamic motions that mimic the activity you are about to do.
Stretching for flexibility (Static/PNF/Ballistic) - Done after a warmup, workout, whatever you want to do to ensure that your muscles are warm and loose. 3-4 times per week, 30-40 seconds per stretch, two sets. Anything less than 30 seconds won't really provide a benefit, and too much more can risk injury.
Static - Reach and hold. Go to where you can feel the stretch, hold, then relax. 2nd set, exhale and reach deeper into the stretch. Slow movements/transitions.
PNF - (Proprioceptive Neuromuscular Facilitation) - Done with a partner, usually. You have the partner move you into the stretch until you feel it, then resists as you tighten against the assist. Hold for 5-6 seconds, then as you relax, your partner stretches past your original stop point. Very intense, usually only done once a week.
Ballistic - Also risky. It can be effective, but carries a higher risk of injury. This is the old style "bobbing" type stretching. The danger is in activating the stretch reflex, which would cause the muscle to contract while being stretched, often resulting in a tear.
So, not really short/intense, not really long/light, but in between.
