Really depends on the application; I’ve been in the cluster for over 11 years now and can use everything.
For PVE I use whatever has the best profile vs the rats I’m shooting. Most of the time I use tachyons, loaded with multifrequency they still out range most rat battleships (only gurristas can regularly hit beyond 45km or so), and out damage megapulse loaded with scorch at equivalent ranges.
Weapon systems capable of longer range let you apply damage to more rats without repositioning; for this reason I like rails better than blasters. In regards to projectile weapons ACs work well in L4s because of their long falloff, but you do shoot a lot of ammo, and you only see max dps within 3.5km or so. The cycle time on artillery is atrocious (though this also means you use way less ammo), the tracking is horrible, but the alpha is amazing.
I want to make a small side note here in regards to medium sized turrets (i.e. cruiser and battlecruiser turrets). Projectiles are borderline garbage tier for mediums; they are only good on the sleipnir due to the double damage bonus, and loki due to the high damage bonus, as well as application and projection bonuses on the turret offensive sub. Medium energy turrets are a bit strange; beams all do more dps than pulse does (even the quad lights, though they have terrible application and projection), you just have to make the reduced tracking work for you.