Is it Annihilator or Fomalhaut?
https://www.bg-wiki.com/bg/Shit_is_situational
Arma beats both of them in perfect setups for raw dps.
Foma is best for Last Stand spam with light chains
Anni is best for high acc needs or times you need enmity control.
Also things that aren't guns exist:
Gandiva is best raw damage bow, it has higher physical damage than all but Arma, but is easier to realize it's potential due to Jishnu's activating AM3 and longer trueshot distance. Tradeoff is accuracy.
Gastra is best Trueflight weapon and decent at physical dps with am3 up.
Fail-Not is a solid bow for Jishnu's spam.
Yoichi is the highest acc weapon in the game for ranger and great for namas and jishnu's and has decent enmity control with namas.
RNG has one of the highest number of RMEA at 7, don't limit yourself by asking the wrong questions.