I hear a lot of talk about sniper rifles, AMRs, etc., but I haven't heard much about the Cowboy Repeater. I've actually used this gun for most of the game so far (I'm level 32ish). With hand loads, you're doing 40 damage (with -3DT on top), 50 if you take cowboy (though that perk has some steep requirements). It also has a bit of a crit bonus on top of it. Fully modded you have a decent rate of fire, decent capacity for a rifle (11), and would only be 3.5lbs (if that mod worked). Just for the heck of it, I took it out to do some sniping. The lack of a scope is a bit of a drag, but I've made quite a few decent shots with this weapon. I'm about to swap for the All-American, but this gun has lasted me 30 levels, essentially all of vanilla. That's pretty impressive, frankly.
I always go for the Brush Gun at level 16, for a rifle. Its just a beast. But I recently picked up the unique version of the cowboy repeater, and it comes with a scope. Its actually not to bad with hand load ammo and the cowboy perk. Still doesn't touch a brush gun though, and ammo isn't scarce at all if you know where to look, or how to make them.