In terms of how 'game changing' it is for the job:
Rng [Gun] (OP) > Drg (Can SC MUCH easier) > Run (Can DD) > Cor (Can physical WS) > Drk (Can SC) > Sam (Apex god) > War (Can SC), Thf (Easier to DD) > etc
Edit* "Can SC" = Can SC for Content instead of just WS spam.
Marsyas and Lionheart are job-changing weapons for 2 top-tier jobs. You have to put those up there. Trishula isn't game-altering but it's a Big Deal for dragoon.
I can't name 2 others. I mean Doji? With R15 Masa now a thing? Doji seems relegated to situational use. Fomalhaut is a good gun but a bit situational too, no? Heishi is great but ninja is a bit niche. I don't know anything about Chango, couldn't speak to that one.
#1 Marsyas (with the caveat of also needing Relic and Empyrean instruments)
#2 Chango: one of the best DD in the game, should be the best weapon WAR has in terms of both SC and pure WS spam at r15
#3 Dojikiri Yasutsuna: has an argument for the best SAM weapon, and one of the top DD in the game.
#4 Lionheart: game changer damage wise for RUN, but can't really be higher since for most relevant content you should probably be using Epeolatry.
#5 Fomalhaut: Great weapon, however, in most situations it is outclassed by Death Penalty and Gastraphetes respectively.
Horn - nothing like a 2 for 1 deal for brd
Trisula - probably the best weapon for Drg
Chango - same for War
Fomalhaut - this is probably the biggest game changer for both Rng and Cor. If you can only select one ultimate weapon, this is probably your best choice not because it is strong but because it's a well rounded weapon for both jobs.
5th one is iffy. Doji looks good but you only use it for SC purposes and Masa might just work as well. Lionheart seems okay but a Drg would probably do better than DD Run.
Lionheart seems okay but a Drg would probably do better than DD Run.
I'm... not sure that this is true? Assuming a fully-buffed melee zerg? Usually when I've seen RUN fully-buffed they are doing a hybrid-tanking role rather than full dps, and Reso with Lionheart pumps out huge numbers, so I honestly don't know.