10 Steel or 'special-metal' Large Serrated Disks in a trap will sever almost all limbs almost every time; I've never had them jam in my experience (though it may be possible). They actually attack 3 times every time they get triggered, making for 10 of them to cause a LOT of stuff to be cut off.
10 Silver (or modded Platinum) Spiked Balls in a trap cause massive damage through armor (though they won't penetrate; works nicely for softening up enemies for your military to finish off) They cause impale damage normally, but if they fail to penetrate armor, they count as blunt instead. Steel also works fairly well for these.
Corkscrews and spikes (also spikes in an upright trap) I personally stay away from. They do a lot of damage, but have a high tendency to jam, which (if you haven't forbidden your traps), causes your dwarves to try to unjam them.
Cage traps are just overpowered. Need a new cage each time it's triggered, but that doesn't really matter when you can catch almost any creature 100% of the time. Giants and seiges get stuck in the traps very nicely, which you can then use as live training dummies for your units. (you can strip them of armor and weapons first, making them ineffective against any of your armored soldiers)
Stone traps suck. Must be reloaded after each triggering, and cause little to no damage.