Quote:
Kannagi
Rhongomiant
Gandiva
Needs more context, particularly what other weapon options the player has for NIN RNG DRG. The answer to which weapon to pick is highly dependent on whether it's going to be a supplement to other choices for niche situations, the player's only RMEA for the job, whether you're leaving something much more impactful for another job on the table, etc. With that in mind:
Gandiva
It's a strong bow, and in niche situations like Gaol v25 it has a place (as mentioned above). However, a couple major downsides:
(1) Archery is usually worse than Marksmanship (both in overall DPS and flexibility - i.e., Gandiva is physical damage or bust, whereas Marksmanship has solid phys and magical WS options), and
(2) To make the most of Gandiva you'll also need another RMEA (Fail-Not, so you can generate Chrono Arrows which are usually the best ammo for Gandiva)
So, for a RNG who already has Marksmanship options covered and doesn't mind getting an Aeonic bow for the ammo, I'd say go for it! But if this is your one-stop shop for a RMEA, don't go with Gandiva first - I'd suggest starting with the much more flexible Armageddon or Fomalhaut. And honestly you'll likely get more use out of Annihilator and Gastraphetes too, making Gandiva a 5th place option. Still probably the best bow though!
Shout out to forum member Demhar's excellent 2021 video comparing all 7 RNG RMEA options:
https://www.youtube.com/watch?v=rS6IMgv98ks I think this is still pretty much spot on, aside from maybe some specific cases in newer content (e.g., Gaol v25, maybe some specific basement Sortie NM, etc.)
Kannagi
I'll preface this by saying I have every NIN RMEA at R15 and I love my Kannagi. But it is pretty clear that it is not the best RMEA to start with. You can't really go wrong with a Heishi as an all-arounder for anything a Ninja would want to do, including hybrid WS. If getting Aeonic clears (or prioritizing other Aeonic weapons) is an issue for you, Kikoku is also an excellent choice - cheaper than Kannagi, useful in more situations, and more uses for its associated WS.
Kannagi is a niche weapon, best used in situations where for some reason you want (a) heavier white damage (e.g., the recent moogle ambuscade where you spend a lot of time dealing with Amnesia), (b) you need to focus on Blade: Hi due to a specific SC with others (if not, you're better off using a different WS), or (c) for some types of crit builds. It's fun when it works, and it's not BAD in other use cases (in most situations, DPS is relatively comparable to Kikoku)... but as an all-around option, Aeonic/Relic are the options you want to look at first.
Maybe Kannabi because you can still offhand it?
No. Kannagi has never has been, and likely never will be, a useful offhand. Other 1h Empys - specifically Twashtar and Almace - have been good offhands in the past, but they have a very useful DEX stat. Kannagi's AGI provides minimal benefit to anything but Blade: Hi (other advantages like Eva or Racc are very minor), and if for whatever reason you need to focus on Hi you should be mainhanding Kannagi, not offhanding it.
Rhongomiant
I'll defer to the more expert DRGs on this, but seems to me that the general wisdom is more that Rhongo is another one that is maybe a niche choice with some useful situations, but not the usual recommendation for a DRG to go for as your first RMEA.
Trishula is excellent and I think is still the most commonly recommended polearm. Beyond that, DRG gets some great use out of Ambuscade weapons: Naegling is (unfortunately?) a great DRG option, and Shining One is basically an RMEA class polearm (on the lower end of that group).
Ryunohige also seems to have made more of a comeback lately in terms of community opinion, and can definitely be put to great use in the right situations and hang with the top options. It's also probably the most obnoxious to make, being a Mythic, and with other "easier" to obtain options (especially Trishula) performing similarly, most people grab those and call it a day.
Also what are the most popular/must have Empyreans these days?
Must-have: Daurdabla, basically seen as a requirement for a serious endgame Bard.
S tier: Masamune, Verethragna (for MNK, not so much for PUP), Caladbolg, Twashtar (for THF DNC, not so much for BRD). All of these are seen as excellent choices for their jobs in nearly any situation.
Armageddon is maybe not as unanimously accepted as that group, but pretty close to that top tier too and has become more popular in recent years with some strats on more current content (e.g., it's great on Arebati) and the addition of Hover Shot (disgustingly good white damage with Empy AM3 up and RNG Hover Shot stacks).