I upgrade to the biohazard path, the poison weakens the enemy (makes em do less damage) and the poison also makes them not able to heal. The charge attack explodes em away and does AoE damage and does poison. I say catalyzer is best. Pulsar is good for crowd control but charged catalzyer shots also can deal great damage and uses for crowd control. I SAY CATALZYER!!!!!!!!!!!!!!!!!!!

I know that explosions from both types of Roarmulus guns will reliably flinch Gun Puppies and Polyps. I cannot confirm, but am pretty sure, that for both guns they do the same for Howlitzers and that non-explodey hits do not flinch any turrets. I greatly enjoy both types, but I seem to be more gun-oriented. I'm leaning toward recommending the more popular Pulsegun since you asked specifically about turrets and it looks like you're really sword-oriented.

The Pulsegun's more of an easy-to-use solution for being able to handle anything, a ...ah, let's say, queen-of-most-trades but absolute master of shutting down turrets. The Catalyser, OTOH, is for people who like to fiddle around with their guns more. Any one can pick up a Cat and get decent performance right away, almost like a Blaster, but to get a lot out of it you have to really get to know it. If you often play in parties, the Pulsegun might be harder to use properly since it can be really easy to accidentally push monsters with the explosions. I myself rarely use either of my Pulseguns outside solo play.

Partly (but not entirely) because you've got so many Elemental-dealing swords with very reachy charge attacks, I recommend the Normal Pulsegun over the Elemental one. I'm sure you'll see peops pointing out that Elemental damage is better than Normal for turrets, but for the Pulseguns it rarely matters due to how the expanded shots just completely lock turrets down. There will be times when you get enough turrets placed such that you must draw aggro from more than you can lock down at a time, but in those cases either you can back off a bit and take it slow or you're probably better off whipping out a sword; if you're unable to avoid getting hit, destroying threats ASAP becomes top priority until you regain ability to avoid getting hit. The difference between the Normal and Elemental versions when attacking turrets is only one or two hits, anyway.

IMO, that damage difference is more than outweighed by the Normal one having much more useful knockback. (the Elemental one's Shock randomly blocks the knock) It comes in really handy for forcefully shoving huge piles of monsters back. It's even powerful enough to shove Trojans and the big red Lichen Colonies into a corner and pin them there. The knockback is in addition to the flinch power that Magnicth mentioned, so with the Normal one you can just push through those giant mobs of Gremlins and they'll be constantly unable to do anything about it due to the flinch. They're even flipped and tumbled while they're flung away from you, like snow before a giant plow.

You might also want to find some videos on youtube to compare the sound effects, as well. They're very different, and I find the Elemental one's sound to be unpleasantly harsh but the Normal one's is fine.