For a brutix, blasters, usually heavy neutron blasters (which are actually a medium sized turret) seem most popular. Use EFT to make sure you can actually fit them and what else you want, if not go for ions.
Rails may be more effective in missions, but a) you'll struggle to fit them, and b) it's just not brutix-like!

Azual Skoll - Eve University/Azual Khan - Advent Nova