Dragonfly Spec Targeting Adjuster Minor Spec Would be the ones I'd consider. Though I think Dragonfly Spec is the most popular one. Since, well... If you'd put Dragonfly Spec on any weapon, you'd put it on the one that literally has an intrinsic that makes Dragonfly stronger...

Dragonfly spec is best. Because you're leaning into the the crowd-control function that the weapon is built around. The only other one I'd use is Targeting Adjuster....but only if you're having difficulty landing the headshots necessary to get Dragonfly to proc.