I have not changed Boone's defaul;t weapon since he started following me....but I am thinking about getting him an Anti-Material Rifle for Christmas.
I don't like the Anti-Material for Boone. The .50 ammo is a lot rarer/more expensive than the .308 and it's a quite noticeably slower firing/loading than the SR. If you don't want him to use the carbines Boone does better overall (imo) with the faster fire rate/higher dps of the SR. He loves Oh Baby and giving him the Chainsaw is hilarious. He likes frag grenades too.
I equip Raul like I do Boone. If I didn't have the reload/freeze bug I'd give him something else, but, er....
Arcade does best with his default gun. Everything else uses so much energy ammo hard to keep him well stocked. But the gauss rifles (or unique variants) certainly work well for him...give him those when hunting deathclaws maybe. I gave Knock-Knock to him once, that was amusing.
Veronica (or any of them really) was great with Pushy but I never keep her or Cass long enough to try more.