Medea, Queen of Farm and things with 6.4m HP (T4 Solomon)
So, if you want to get things done quickly, Medea is simply your best bet. Almost everything that you need to farm has fairly low HP, and Medea will just kill it for you easily under AAB. This includes things like Advent events, raid events, Labyrinth events, Standard/Expert Disaster farm, daily quest/Fang farm, and so on. Probably even Ultimate Disasters. Because of this, I highly recommend that you get Medea first for your strongest element. She will simply speed up your gameplay significantly. Additionally, she is freaking amazing in Tower, capable of soloing the majority of floors. If you're going to get more Medea Glaives, it is going to be because of Tower.
Builds:
Low tier content farm build: 2-A, Desertion (Asmund EX skill)
While not really capable of the best of her damage output, this build will oneshot daily quests and low floors of Labyrinth with AoE damage.
Medium tier content farm build: 2-A, Solomon Ring (Solomon EX skill)
Still not really capable of her best damage, it should be enough to AAB kill most Advents and other stuff with more HP, just taking a longer animation time.
High tier content farm build: 2-B, 3-B, Hourglass MEX
This is what deals her most damage, with 1m+0.7m+1m+0.7m+3m = 6.4m damage being very, very easy for her. But you will probably need to manual her for skill order for this to happen. Useful for clearing stuff like raid event Experts in a matter of moments, T7 Accessory quests, higher Tower floors, and so on and so on.
Debuff build: 2-B, 3-B
While unlikely to see much play, it should be noted that Medea is extremely versatile. Do you want -20% Elem Res, and -20% of your elemental strength? Well, here you go. Medea has you covered. Use Hourglass for double the applications against debuff resistant content.
Strong team speed-up build: 3-C, Hourglass MEX
Want to play some serious content (aka non-farm) with Medea? She can do that. Being able to give your team -2 ability CD is serious shit, all the better the stronger your team is. While she is unlikely to be better than Yorimitsu, she will still be extremely strong in any content. Assuming that your team is strong of course, giving a SR team -2 ability CD isn't going to do much!
Yorimitsu, Queen of Damage and one-shotter of things with ~16m HP (T4 Shingen)
Without a doubt the strongest Soul in the game right now. Interestingly, while PF was what Shingen be the strongest Soul of her time... ... Yori's improved PF doesn't really do it here. What really makes her shine is her incredible 2-A skill. It turns out that when you buff a 25% combo skill with 2/8 uptime into 40% combo with 3/7 uptime, it is PREEEETTY FUCKING GOOD. And then they also slapped +30% burst gain on top of that, jesus. As such, any serious Yori build will always make use out of 2-A. Also notice that Yori has two different builds (which really just amount to the degree of laziness that you feel like at that very moment). We will eventually get tons more team slots, and when this happens, you can make both the Yori builds for ALL elements. I highly recommend that you get Yori Lances for all elements or at least all of your strong elements.
Oh, and it should be noted that Yori's ability to go above 100 burst meter while only expending 100 burst during Bursts is EXTREMELY helpful. Seriously, you won't believe how much you'll want everyone to do the same once you get used to that shit.
Builds:
16m+ HP farm build: 2-C, 3-C, MSD MEX. (aka Wham-Bam build)
While not a serious build due to lacking 2-A, this does allow for a turn1 Full Burst without Burst Hour. Making this a very good build for farming Ultimate Disasters if you can be bothered to manual. It will deal 16.25m damage off-element and 19m damage on-element... assuming you can reach 2m burst cap on everyone in the team. Not exactly easy, but significantly easier if you go full ham with Vigor builds in Water and Thunder.
Anyway, during Burst Hours, this build turns into the Wham-Bam build. Just do two Full Bursts in a row. You can do this in a raid, hit "Go to My Page" button, and do it in another raid. Once you've done this in three raids, the first one will probably be dead already and you can collect your purple chest. Sweet.
Wham-Bam-ThankYouMa'am build: 2-A, 3-C, EI MEX.
This is a Burst Hour raid MVP stealer build. Turn 1 Full Burst, turn 2 2-A and EI and you're virtually guaranteed to reach Full Burst in 3 turns. Then buff up, Full Burst, 3-C and Full Burst. If you're strong, it is extremely difficult to take MVP from you after three extremely fast Full Bursts (turns 1, 5 and 6 probably). Then you can either move on to the next raid, or keep AABing. With 2-A and EI in the play, your damage output will be just dandy.
Outside of Burst Hour, it largely plays the same way, just that you get "only" two Full Bursts, this time on turns 4 and 5.
This build has largely changed Kamihime raiding a lot. It is quite frustrating, because if you host and nobody joins, this build will probably fuck you up since very few people are able to solo raids with a purely offensive Soul. Meanwhile, if you're the one joining and see quite a few people in the raid already, you can choose to go with this build and grab an easy MVP. So... MVPing your non-hosts is now actually easier than your hosts. Geez. Welp, on the other side of the spectrum, Yori leechers will do quite a bit of damage for you and your raids will be far faster. So that's nice, I guess.
Theoretical Yori Bow build: 2-A, 3-B, EI MEX.
Meant for Yori's Bow users, I don't think that this build will really see use. Still, with Yori's bursts only costing her 70 burst, she will upkeep a pretty decent amount of Special Attack. Go with Lances, people.