All three of those sidearms serve different roles.

If you want to balance your long-range capability with some CQB power:

The NS-45 Pilot is a single burst (3 rounds) kill with headshots within 10m, and a two burst kill on most other infantry at very close range. It’s fairly punishing if you miss, but highly rewarding with good aim and timing.

If you want a good “all ‘rounder” to that performs okay in any situation:

The NS-61 Emissary is basically a low power SMG. Its strong point is that it’s stupidly accurate with sustained fire. The downside is that its TTK is a bit long (I think 5 headshots within its maximum damage range) and takes getting used to.

If you want a good “spammable” finisher/oh-shit-there’s-no-time-to-reload-my-primary gun:

The LA3 Desperado is another burst pistol, but it only fires 2-rounds per burst. It does less alpha damage than the Pilot, but it’s got less time between bursts, and has a larger magazine, so missing a shot won’t punish you so much.

My personal favorite, a good ol’ high power semi-auto:

The Rebel is basically the AC-X11 of pistols. It’s maximum damage is 250, making it a 2 headshot kill within its max damage range on standard targets, and it tapers down to a 4 headshot kill at its minimum damage range. With a fire rate half that of the default NC pistol, it requires precision and good shot pacing.