On my current destroyer, I use 3 long range 280mm artillery cannon, and 4 short range autocannons, 2 200mm and 2 150 mm. (although due to powergrid limitations only 1 150 is active right now). And I also have a missile launcher, but that doesnt really count. I was thinking of removing the 2 150 and adding one auto cannon and one artillery, but since I'm saving for a cruiser, I'll ignore that for now. On most drone missions, only my artillery fires (28 km away kills feel good.) If a ship does get in my 5 000m radius, it gets a taste of my auto cannons. Since I am liking more and more the battleship approach of killing without drawing circles around a target (and really, with my kill speed, my mobility is pretty useless), I am going up in size. I believe that a good balance between long range and short range is good. (However I'm a fighter, with lots of skills that improve my precision and tracking speed.)
Edit: Not fair, he gets cash offered... Oh well, my goal for tonight is to make 2 million isk. My current estimate was adjusted to 16 million isk for a geared up stabber, and that may change since I may go with electronic warfare modules instead of the last two high slots being missile launchers)