The big advantage of hangars? Range. They can hit anything in the gravity well, unlike guns which have to be placed? Only 1 way into the system? Guns may be the way to go. 5 phase lanes into the system? Maybe think about hangars.
The big disadvantages of hangers?
~Low damage output for the number of tactical slots that they cost.
~Easily countered by flak cannons, special skills that cost only 100 anti-matter, and enemy fighters.
~Are only really useful against LRM's, Siege Frigates, Fighters, Bombers.
~Hangers are flimsy, and once they're gone, your squadrons start taking damage fast. Once they die this time, they're gone for good.
~Hangers are a priority structure target AFTER Turrets. If you don't have any turrets up, your hangers will be the first thing attacked.
~Advent and Vasari Hangers cost far - far - far too much.
They're useful. They're just not useful in huge numbers like everybody thinks. Turrets and Repair Bays are better.