As our group allows Pistols to utilize the Accurate Weapon Trait to its full potential, I'm partial to the single-shot "Valentine" Dueling Las with a Hot-Shot Charge Pack and a Red-Dot Sight.
Sorry to be that guy with the rulebook, but combining a Dueling Las with a Hotshot Pack ain’t a thing. The weapon’s entry in the Inquisitor’s Handbook makes note of the Valentine’s special power cell already being a unique form of hot-shot.
The good news is that Belasco Deathworks makes a Dueling Las that is not only more powerful, but can accept a Hotshot, or at least says absolutely nothing to suggest that it can’t. That one’s in the Rogue Trader Corebook, though.