A purple Px4 Storm Type F with Coolheaded talent.
This is a great sidearm that reduces all skill cooldowns by ~3% on a headshot, making it a great support weapon.
Coolheaded triggers with all red damage, i.e. frag bleeds, fire nades, shock nades, etc.
Only other weapons that can have it are DMRs and Caduceus. The latter might never drop for you, and DMRs can have better talents, so getting a pistol with Coolheaded is a great compromise.
Just get it. You never know when you might need your skill back in a jiffy.