There have been multiple posts and debates about this already. Please search the forums before making posts about endlessly-discussed topics like this.

That said, Catalyzer is good only when you use the charge attacks; if you plan to use it like a normal gun, get a Shadowtech instead. As for the charge attacks, Catalyzer is super-slow, and detonating charges takes forever. If you run in a party, there's a good chance they'll kill two or three monsters before you can detonate one--they'll probably start attacking the one you're targeting anyway, ruining you.
If you run solo, Catalyzer is a great weapon because you can use your own tactics and develop advanced techniques for playing with it -- if you want to do hack-and-slash or run with other hack-and-slash people, don't bother with it.

Pulsar deals great damage all around and quickly handles most enemies. The only downsides to it are that the bullets are slow compared to the alchemers (but faster than Catalyzer) and that the explosions potentially send monsters flying all over the place. It's like running around with an infinitely charged calibur. It handles monsters well, but you can also easily screw up and get everyone (yourself included) killed.