You'll find one of the best weapons at the museum of history, Lincoln's Repeater. Fires .44 magnum shots, and has the highest damage per shot of any small gun. You could nip on over to evergreen mills and get The Terrible Shotgun. A point blank sneak crit from that weapon will kill anything in one hit. However my favorite weapon is the Victory Rifle which is a sniper rifle behind a level 100 lock near Rockbreaker's Last Gas. Any time you crit it knocks them on their back. You may not have 100 lockpick, but its reported that if you have a Dogmeat, and tell him "get me a weapon" he'll bust into the locker and get it out for you. Dogmeat is baller. No other quest gives anything worthwhile, really.