Rivens are silly.
Made after rolling this insane Riven. Quickly became my personal favorite automatic fire rifle, which I use for all end game content sans Eidolons.
Pros: High Riven Disposition (1.3 or 4/5 dispo dots). Expensive, but with enough forma you can modify it to meet the needs of multiple scenarios.
Cons: Expensive. Spin-up fire and slow reload may be off-putting to those accustomed to "smoother" options like Tiby Prime. Requires a solid riven to reach S-tier.
Variations
This Corrosive variation I made for high level Grineer Lich farming. I go back and forth on whether I prefer Hammer Shot, Heavy Cal, or Thermite Rounds in the 7 slot. Leave me some comments and help me settle the debate.
Swap Malignant Force for Rime Rounds (Magnetic) if headed to Fortuna/Jupiter.
If running lower level missions where sustained DPS isn't as important, swap out Hammer Shot for Vigi Fervor or Shred/Vile Acceleration if running Vigi mods in your Sentinel.
Other popular choices like Viral + [Hunter Munitions] are still viable, but the lack of Slash damage puts the HM a bit behind on this gun at high levels, at least it feels like it to me.