I managed to get all of the new syndicate primaries and level a few up. So far, the Tigris seems like the big winner. The rest are all mixed bags...Boltor not as good as Boltor Prime...Penta not as good as Tonkor...Hek can't use the syndicate mod. Not sure about the Simulor, but I never knew what to make of the original either. I'm not a bow guy, but I do love the look of the Cernos...not sure how it holds up to Paris/Dread.
In terms of just "fuck you" numbers of damage, the S.Tigris wins. It's an upgraded Tigris! The syndicate effect is also good.
Penta can be as good as the Tonkor, and the Radiation proc is nice. They are largely competitive with each other and you don't need to be reloading all the time like you do with the Tonkor. Just watch for self damage.
V.Hek is an interesting case. If you have Primed Ravage it blows passed the regular Hek. The spread is tight enough to start doing headshot crits with it. Even with regular Ravage, the V. Hek can out damage the Hek, and you don't need to eat up a mod slot for the Syndicate effect either.
Simulor is godlike. With enough effort, you can be doing millions of points of damage by putting the orbs up a little so that the pops will deal head shot damage, plus you get minor CC with the vortexes it generates. The explosion radius when the orbs collide is way larger than the normal version which helps immensely. The syndicate effect is alright, energy regeneration is nice. About the only bad thing for this weapon is the Magnetic damage.
Cernos might be the new king of the bows. Not needing to use a space for fire rate is insane, and while it might not push red crit potential, it still has a crazy high crit chance. The syndicate proc is equally powerful. Yes it's Impact, but on a team without 4xCP in void missions, it can easily push passed the Dread thanks to the proccing and fire rate.
So basically all of the weapons are good. The Boltor debate is going on a bit longer because there is some firing sustainability to consider with that larger clip, but the proc isn't anything to write home about.