I tend to prefer Full Auto Assaults. Can hit up to 7 targets in a 40 degree cone (I think). Proc rates on weapons in STO are kind of hard to figure out, but if it's a per hit proc rather than per salvo proc, then I've got multiple expose chances per target from each usage of Full Auto Sweep. Full Auto Assaults also pair really well with stacking debuffs, since multiple projectiles are striking the target.
I tried using wide beam pistols on all my BOffs, I don't think I've ever had so few exposes, the problem seems to be that the attack range on a pistol is ~30m and the attack range on the wide beam is ~15m, which means that the officers never really go in good range to use the special attack. I had a few very close quarter encounters on space ship missions where the wide beams gave a good result, but for any big area combat, especially planets, the wide beams was just awful as an expose weapon.
I'm going back to using a full auto assault, in the hopes that every hit has a chance of triggering an expose.