For a first weapon, Pulsar > Catalyzer.

It takes less skill and patience to use, and also does far too much more damage.

Sorry, should have clarified: Too much damage for a rage-inducing spam weapon which does Shock.

both lines of both guns are great, But like all weapons its "different strokes for different folks". I love guns and bombs myself over swords however i find myself avoiding using the pulsar gun lines in "foreign groups" and sometimes find myself getting highly annoyed with other people who do.

I only use the pulsar when i play with guildies whos play styles i am familiar with becuase the gun can get "messy" and in the wrong hands and "selfishly" used it causes more problems than it solves for the other members in your group. There is nothing more annoying than getting dropped becuase the guy with the pulsar is being a goon "spraying and praying" all over and pushing the mobs into you.
However used effectivly it can provide some serious situational support as you can cram problem monsters and even groups of them into a corner to be finished off by sword charges or whatever your pals are using.

In my opinion the cat guns are more geared to "support rolls" as they require a charged shot followed by an ignition shot to deal out its maximum damage, but the resulting explosion does throw the mobs around a little bit. Cats can be used in close quarters if you are proficiant with dodging monsters and are good with "shield charging" your weapon becuase letting off an accidental ignition shot and tossing monsters into your own escape path can obviously prove problematic. The poisen line of the cat is super sweet for groups hiding healers in them especialy the butterflies which sometimes can be tricky to single out. Charge up a few rounds into the group, send out your ingnition shots and you will have poisend and scattered half the group. If you are quick you can kill most if not all of them before the poisen wears off and they can be healed again, or use the scatter to rush in on the healer.

You have to follow a weapons path you feel comfortable with using. Yes these guns are awesome, and used wisely people will love to do runs with you. Used poorly and you will be avoided like the plague in missions and arcade runs for getting your buddies killed more often than they can handle with messy explosions and chaos everywhere.