I'm in the gauss cannon camp.
All these other things you're possibly putting on are extra HS, which could be more efficiently dedicated to more gauss cannons, which will on average give you more missiles destroyed per HS than these other options, assuming equivalent research.
Of course, if you've left gauss in the dust on research because you thematically want something else, that's fine, but it's not an argument from optimization.
This maybe goes out the window if the enemy is using armored missiles; in that case mesons may be optimal for a narrow band of missile armor. I haven't run those numbers yet, because that model is complicated and I'm busy.
Edit: I should add that, while gauss are the optimal point defense weapons, that doesn't mean you should never use others or anything silly like that. It makes perfect sense to, e.g., build meson/railgun fighters and use them as multi-role, where one of those roles is PD, but they're also capable of neutralizing enemy FACs/light craft or doing bomber escort, etc. But just strictly for point defense, gauss guns are best per HS/research.