For me it would have to be my trusty DMR. You can zoom in on targets and pepper them with more accurate shots than the assault rifle. The downside though is they lack ammo whenever you first pick one up though.
Grenade Launcher is by far my favorite weapon in Reach. Getting aerial kills on players flying around with jetpacks makes me feel godlike.
I initially thought I would love the pistol but the recoil bloom was too much for me and made it a CQ to low-medium range weapon.
As a side-note I just got to playing Reach’s version of Griffball and I love the new Hammer. Can’t say the same for the sword cause of how badly it got nerfed. It’s practically useless in Griffball, especially with the slow weapon switching making hammer more useful.