Hikaru as a lyricist is stellar. You wouldn't even be able tell she's an amateur with how she writes super catchy lyrics also convey meaning. I already like her lyrics more than what Kajiura-san has put out in the last few years, though Hibari and Haru wa Yuku are very good lyrically. Wakana has a ways to go(like with "breathing", where you can tell that the lyrics are very amateur-ish), but she's steadily improving, with my favourite being Happy Hello Day, lyrics-wise. I need more of Keiko before I can give an opinion, but Inochi no Hana was fairly generic.
In terms of debut singles, Hikaru's the most appealing with a catchy hook and her signature rough-around-the-edges rock voice, followed by Wakana and Keiko who I'd say are equal - Wakana has the better songs, Keiko has the better voice.
In terms of repertoire, Hikaru's is more diverse, though steadily in the realm of Jpop. Avaricia, fili and Existence from her first album are all A-grade songs, IMO. Wakana has more songs overall (2 full albums within the span of a year is a lot), but there's a lot of hit and miss material (the misses being a lot of her slower songs). I'm praying for Keiko's album to be a lot better than her debut. She had the potential to dominate, but this music is ehhhh.
Tbh Hikaru's lyrics for alternate is very in your face about the anime content and i always laugh at certain parts due to how blatant spoilerish it is. On other songs her lyrics are pretty good tho tbh they're fairly generic shounen-animeish as well.
About songs, Hikaru's songs are very anime-ish. While the other two seem to steer away from their anisong singers root, Hikaru seems to embrace it as she's also the biggest otaku between them 3. Tbh music wise Hikaru's songs are kinda boring in a sense that they all sound almost the same. Hikaru's very limited range ever since 2015 also hinders her capabilities as a singer because it makes me feel like almost all her songs don't have certain oomphs, vocal-wise. They're all carried by the instrumental or how the songs are arranged. It feels like she can only sing G4 at highest. Anything above that she strains or simply failed. Sad.
Wakana's music is actually more of my taste and magic moment album shows how much she's improved as a solo singer. In her first album there are some pretty good songs that are hindered by her vocal issue, like Yakusoku no Yoake (very sloppy vocal performance but the song is fairly hard and kinda out of Wakana's also very limited tessitura, though hers is not as limited as Hikaru's). Kinmokusei(?) and some other songs also have this issue. On magic moment album though, she showed excellent songs choice. The songs are pretty much in her tessitura, she sounded more relaxed singing them (though relaxed is a loose term as Wakana tends to constrict her throat when singing), and Wakana successfully belted in some of them. Girl needs to work on her head voice though, she still sounds like chicken whenever she tries to use them. magic moment album itself is imho excellent and is much better than Kalafina's fotw.
Keiko just needs to work with better producers and composers. I'm waiting for her album in September that hopefully will have some good/decent songs. be yourself showed that she has the range and inochi no hana showed that she's great at singing on the register people know her for, but both songs are just very mehhhh.
Kaori is the same with Keiko. A fairly good singer stuck singing meh songs. I don't hate her songs but I don't care for 90% of her discography. They're almost all fairly forgettable.
Yuriko's solo is snorefest at its finest. Sad. They're all kinda good when you're trying to sleep though due to how sleep inducing they are. I don't think I liked even one song from her Kaiida mini album and her other one mini album. I'll give them another try tonight and refresh my memory.
I for myself do not care that much for the text but how the song is performed. About the three Kalafina Girls i cant say that much except that i liked Hikarus "Determination" and i loved Keikos "Nobody Knows you" since her deep voice was good in display. About Kaori, i think she could have been more successful if she had decided to make for Brilliant World and Calling atleast a PV or started her Solo-Career a bit later and went to another Label than Team Entertainment (one that makes you known to a larger audience with maybe ten times of Fans then the Label she is now). I mean the looks and vocal talents for kinda succesful Jpop does she have, so why not. Is she really so much worse than most Japanese Singers and even most Westerners are not that good. But maybe my Bias speaks out. I find it kinda funny, that every singer that worked with Yuki before they get a bit known does not be succesful when they are without Yuki, although the Kalafina Girls i think did not start too bad. PS: I think there are some songs per Kaoris Albums that i think that stood out for me (Place: Honki no uso; Colors: Addicted, Escape, Grasps; Make it: Change, Trap; Gift: Working, mindscape, savanna no hayate, stole my heart, theatrium, run-limit; Flowers: Alstroemeria, Inori Megurite, Cleome, Blazing Star. I also liked some of her songs that were not that much related to her Team Entertainment Songs like her Onizuka Songs or the Gunslinger Stratos Songs etc..
Now that all 3 have solo albums (technically Hikaru had some but they were strictly limited releases), I can compare their works so far, since it's also been, what, 4 years since Kalafina's disbandment.
Hikaru has some my favourite songs among the 3 (granted I'm a big fan of anison so that's not a surprise), but on a whole her discography is dragged down by the same-y boring indie songs she releases on YouTube, and her vocal technique. Her first album is a solid 7/10 but it could have been a lot better with more album-original songs instead of recycling her singles and B-sides. While she's singing in a much lower tessitura than during Kalafina, she can't control her voice with dynamics (it's either a terrible soft voice or a terrible loud voice) and her lack of range prevents her from singing better songs since there are only so many melodies you can make with one octave. I like her vocal performances in Avaricia, Ambient Border, Alternate (acoustic) and Gira gira especially, but the rest is a big miss. She either needs a complete vocal reset, or just get surgery for her nodules. Some great songs, most of them being decidedly meh, vocals need a lot of work.
Wakana is overall more consistent. Lots of ballads and with the occasional upbeat song. I like both her albums (Ruriiro no Sora and Ai no Hana from her first album are 10/10 songs, with where and magic moment in her second album take the cake). Even the acoustic album is fantastic (Rain is gorgeous). Her voice has certainly gotten a lot stronger (that belt during the magic moment live actually gave me goosebumps), but her head voice, oy it has declined so much. She doesn't even use it, opting for her much weaker falsetto instead. She just needs to not place her voice so high in her nose, changing vocal placement is singing 101, so I don't get why she still chooses to sing so honkily, on top of losing her vibrato completely. She does this annoying thing at the end of her lines where she drops the note - once you notice it, you can't un-hear it. Overall, her songs are good, vocals are so-so, it could be a lot worse.
Keiko...it's really sad looking at her solo career. While it didn't sell as badly as Hikaru's (I blame that on a complete lack of promotion), Keiko showed the most promise with a solo career since she had it all - the looks, the vocal chops, the stage presence. It's really sad that 95% of her songs are downright bad, either from terrible vocal choices (Hajimari wa and Ray) or just being bad songs themselves (Be Yourself is a walking disaster, every one of her rock songs are some of the worst I've ever heard). The other 5% are great (Tameiki, Tooriame, lost - that's it). She suffers from an identity crisis, since she has no direction or genre she wants to pursue. She has the technique to be amazing in all of them, we've seen that from Kalafina and FJ, but her composers are, for lack of a better word, incompetent. I've read somewhere this is what Keiko likes to listen to, but she can't be serious - her discography is a far cry from the Kpop and Jpop she listens to (she has said she likes Twice and SNSD, but their songs are FAR better despite being mainstream). None of Keiko's songs would even be considered mainstream since they're neither catchy nor listenable. If I had a choice, I'd want Kajiura to be her composer, but not in the vein of Nanairo no Finale, that was bad. Kajiura's recent singles from Lisa, Aimer and Hinano have been so good, like, 2007 Kalafina good. If Keiko sang those kinds of songs instead of...whatever she's doing, she'd be way more successful.
So, overall, Wakana > Hikaru >>>>>>>>>>> Keiko
But vocally Keiko >>> Wakana >>>>>>>>> Hikaru.