I fly the scythe a lot, but i don't have much to cert into anymore, except the last level of flares or hailstorm mag size which i don't think is worth it considering the alternatives. I also have the eridani already, and don't think the sirius is worth getting even though people say it is better. I am considering the Commisioner/Underboss, and things like the AV turret or Parallax. Any more suggestions?
Harrasser (at least for the TR) has been my major cert earner for the past 2 months. Get a buddy and you'll be raking in the certs like no tomorrow.
Every weapon you listed is useful. In order of most useful to least: 1. Sirus 2. Parallax 3. AV turret 4. Commisionar / Underboss
Lasher Lancer if you really want (i got it some weeks ago and of course my Outfit stopped doing lancer squads tha exact day) Av Turret Ursa SV88 VX67 don't get the Parralax except when you think you can get the 1k certs back until they make the Infil Update pistol of your choice, but the Beamer is decent enough, just slap a Laser on it so it actually is laser related
AV turret, by far best certs ive spent (although need to drop some more on to to really make it shine), although it'll eventually get nerfed (rightfully so)