I'll give a rundown of my thoughts of each PD weapon:
PD laser: needs range-boosting hullmods on anything bigger than a frigate really, but is quite good
LR PD laser: What a joke; don't bother with them unless there is utterly no other weapon you can find to put in the slot
burst PD: nice against fighters and single large missiles, but large numbers of small missiles or bombs will very quickly overwhelm them
heavy burst PD: basically an extreme version of the above. Essentially only useful for sniping MIRVs before they split & taking out torps. Also good vs. fighters, but very, very easy to overwhelm.
Guardian: The burst PD idea taken to its logical extreme. This isn't really a conventional PD at all; it is so front-loaded, it makes a poor normal PD, but it is rather effective in a very-low-flux/s anti-frigate/fighter role.
machine gun family: cheap, gets the job done, not the best PD in the world by a long shot, but it has the bonus of being rather effective against shields
vulcan cannon: its like having a bunch of machine guns in one. but with very little ammo
swarmer missile: missiles to take out fighters, though their low ammo count and range makes them less valuable on non-fighters/bombers.
flak:
dual flak:
and thats all I remember off hand