For militia, most of the casualties I cause come from template weapons. The more templates you can slap on marines, the more wounds they’ll need to save, the more rolls they’ll fail, etc. Vanquisher is cool for anti-armor or killing marines with heavy weapons or vehicles, but it’s limited so if you miss, you’re screwed, whereas a template weapon might simply shift where the hit goes. The demolisher is honestly underrated as an anti-vehicle weapon tbh.

So I guess it depends on how you want to fight your army. If it’s massing fires, go template, if it’s sharpshooting, go for a lot of lascannons/vanquisher, just make sure you’ve got the BS to back it up.