Aerith has had a revolving door of actors play her, more than anyone else from FFVII. Despite that, most of them end up having a roughly similar sound and approach to how they play her, which is probably just a sign of SE being really particular about her. Like the rest of FFVII's cast, Aerith is more nuanced than she's often easily boiled down to. The fanbase and the Compilation often fall into a trap of treating her as an angelic, messiah-like figure who has the purity of a goddess. Aerith's not a goddess though - she's human. I'll go into it more later, but that sense of humanity is the key to what IMO makes her voices successful.
Mandy Moore started us off, and all things considered, I actually think she was really good. Though KH1 relied pretty heavily on stuntcasting for its original characters and FF characters, strong voice direction from Ned Lott really helped keep things more successful than not. Mandy brought Aerith to life with a solid, lively performance, setting the stage for each voice to follow. I honestly think it's too bad she never got to continue as Aerith. In the years since, she's had tons more experience in VO and become even better at it. With time, she could have done something truly special. But hey, what we have from her is still pretty good, even 18 years later.
A lot has been said about Mena Suvari over the years, some of which really doesn't bear repeating. But yeah, she's unfortunately the weakest link here. KHII's VO was a step down from the first game's in general thanks in part to a voice director shift from Ned Lott to Bob Buchholz, and Mena's Aerith unfortunately symbolizes several of the worst sins of his work. Her acting was simply stiff, and the tone of voice she was asked to speak in just didn't come as naturally to her as with the others.
Andrea Bowen was a step forward, but my only real reservation about her is it's a performance that's more tailored to Crisis Core, where Aerith is younger, and she plays up the most sense of ingenuity. I like her in the context of Crisis Core, and she probably could have done FFVII Remake considering the amount of time it's been to have naturally grown with Aerith, but obviously we can't dwell on hypotheticals.
Finally, we have Briana White. Remake has the best sense of who Aerith is, and luckily Briana steps up to the plate. Although they do have her speak in an affected register, it doesn't feel forced or hold her acting back. And just most importantly - she gives Aerith the best sense of fun. Her Aerith constantly keeps you on your feet, and has great chemistry with both Cloud and Tifa. And when Aerith gets to be mature, she steps up to the plate - her scene where she revisits Seventh Heaven to save Marlene is so, so good. Briana not only distills each of Aerith's other VAs into one, but leaves her own stamp. Hopefully SE can finally make their mind up and keep someone, cause she's got it.