[Edit: didnt realize there were 2 pages, was probably somewhat obnoxious and condescending, sorry]
Different calibers of lasers are better for different roles, big guns for killing big things, small guns for killing small things. there is no one caliber that is truly better, and you gotta know what you are expeting to face.
You will need diferent ships for different roles, and these will require varying calibers of lasers, so the more options the better. YOU WILL NEED THE BIG CALIBERS
lasers are not the best weapon for point defense though, that job has always been the Gauss Cannon's.
Puting more weapons per turret results in a bit more punch per size, say a single weapon turret is HS7, a quad turret might be size 26, saving you 2 HS. I think they also have more hit points, but dont quote me on that. less redundancy though, so depending on the ship, you might not want to do that.
and if you are ever in doubt, you can always check the forums