I wouldn't completely dismiss Anguta - particularly since you're a career DRK. Send a message to Bloodlusty, Buuki, Ruaumoko and so on about the weapon in today's end game meta before deciding against it simply because you already have multiple DRK weapons.
Many types of content require a job to have multiple weapons and be versatile. Good RNG's will want to have Fomalhaut AND Afterglow Anni because both are needed depending on what you're fighting. And more often than not, you're using Chrono Bullets from Fomalhaut on your Anni anyway (and sometimes vice versa).
If you solo a lot or want weapons that are easy to self-skillchain Radiance and Umbra (and play the respective jobs) then look at Aeneas since you mentioned it.
I know you have COR also so having Fomalhaut would obviously be a benefit to you. I'm not sure if you're using Armageddon or plan on making a DP, but Fomal would definitely help your arsenal there.
Yes, I'm aware of Anguta and its potential in certain situations. I think I've done enough for DRK, I afterglowed Lib and will have AG Rag soon as well. I'm not always playing Dark Knight, so something has to give and I should focus on my other jobs so they ain't stuck in 2014-15 mode. Fomal would be a great boon to my corsair, but my thief is still using Taming Sari's and is my main farming job (when I can be bothered to farm!) so it would boost that aspect.
Personally, if I could make the dagger, gun, and scythe I would, but limitations restrict me to the one choice for now. Whether I pick Aeneas or Fomal, I'll miss the other and secretly wish I could've done Anguta too. Making my Thief more available for high tier NMs is appealing, and since I got Scholar up I'm using Corsair less and less. Edit: I don't have Ranger by the way. :)