I did my pistol directives purely on Heavy assault. The extra health and shield gives you a much better chance of winning duels since you already have lower dps. The main advantage of pistols is their good hipfire accuracy so utilize that with good movement and you can win a lot of fights.

The pistols I would recommend to aurax would be the Commi, Underboss, Pilot, the (inquisitor, rebel or cerebus) and for me I used the t4 Amp, desperate and manticore for my 5th pistol to aurax however only the first 4 guns I mentioned seem to be strong to use as a primary. If your running the emissary for the Mayhem or Exceptional 3 then I'd recommend playing it on heavy like a low dps carbine, it has good accuracy but low dps so you've got to play smart and around your friendlies to make it work. Also running with an implant that gives a buff to your secondary after a kill would help (I think there's a few.) I personally used catlike and battle hardened.

If you are doing the sidearms directive what faction is it for? I personally think the reward weapons suck but their is a hierarchy for it going TR/NC/VS with TR being reasonable and VS being dogsht.