Both games hold a certain reverence for pistols. It’s the first gun you’ll be seeing your character wield in the campaign/heist, it gets its own weapon slot, and it’s the only gun you can use while in bleedout. An emergency weapon through and through, no other gun is as certain to make an appearance in a given playthrough.
Left 4 Dead‘s starter pistol, the M1911, is the only gun that didn’t migrate into the new game, its role instead being filled by the P220. A halfway-decent pistol with a respectable rate of fire and damage output, it can be dual-wielded at the cost of some accuracy and reload speed. The second pistol is actually a Glock, though the difference is only cosmetic. Personally I freaking love the dual pistols because they’ve got 30 rounds, each of which deals more damage than an M16 bullet. It’s like having a semi-automatic rifle in your secondary slot and goes particularly well with shotguns. But the damage resistances can stack up on higher difficulties, and that’s where the Magnum, aka “Desert Cobra” comes into play. The Magnum is the only gun aside from the sniper rifles coded to always one-shot common infected regardless of actual damage output, and it has the same perfect accuracy and penetration power even when incapacitated. Watch any Youtube video of a team attempting Realism Expert campaigns and you’ll probably see a lot of quality Magnum play.
Payday:The Heist really comes into its own designing niches for its four pistols to fill. While the Crosskill .45 and Bronco revolver fill the aforementioned two roles, the B9-S is silenced allowing its use during stealth portions of heists at the cost of damage output once the assaults start. Lastly the STRYK is the only fully-automatic, a machine pistol with a beastly damage output that chews through ammunition but leaves your target a shredded mess. All four fill different roles and appeal to different types of players, and personally I most prefer the versatility of the Crosskill, for most of the same reasons I prefer the duals in L4D2. But as the difficulties increase, it also must bow down to its powerful magnum alternative.
Revolvers are also the only pistols worth using in TF2’s Mann vs. Machine, though that’s only because spy has nothing else that can fill that slot. Every Scout and Engineer in MvM better be dropping their pistols for Mad Milks and Wranglers/Short Circuits, or I can’t imagine their team’s going to be too happy with them. If Spy did have any utility item he could stick there, like the hypothetical Flame Retardent Suit, I’m willing to bet revolvers would bite the dust too.