Cannon/beam can be quite effective and can put a very solid punch into a very small turret.For energy efficiency shy away from missiles. Cannon/cannon/Any effect that aint overdrive
Go for a 50-80% slave, slowfiring autocannon.
Dont use pulse or beam secondaries. Dont use missiles. Beams hitscan ability is unreliable. at least the cannons lead properly
That said, the DPS is entirely dependent upon the number of weapon modules. 100 modules of cannon will have exactly the same DPS as 100 modules of anything else. 100 modules of cannon/cannon will have exactly the same DPS as 100 modules of cannon/beam for instance. The difference is that cannon/cannon doles it out in a great many small shots while cannon/beam put it all into a single shot once every four seconds, which is why it can hit hard when small.
To be sure, some combinations are more useful than others. Missiles need a lot of power storage and can be easily shot down by anti-missile turrets if your don't build your ship so as to be able to saturate your enemy's defenses. Cannons are great and cannon/cannon a good mix for rapid fire. However they are relatively close range weapons and if your enemy is staying at say, missile range, you could be in for a world of hurt trying to close the range.
Cannon/beam however has a very good range. It does need extra power storage, four times your power regeneration, because it effectively stores up it's damage potential for four seconds. This is why a relatively small weapon can still hit with a good punch if it is using cannon/beam. I am not saying that you could not use cannon/cannon and Guthris suggests, but make sure you are in a relatively nimble ship if you do so you can close to weapons range if need be.
I strongly advise using a tertiary effect as part of your weapon. I am personally very fond of the punch effect.