I have just finished the level 20 rememberance services where I met Alphinaud and Alisaie, so I wanted to offer some early impressions.
Y'shtola: Very good.
Thancred: Very good.
Minfilia: Very good.
Yda: Good.
Urianger: Need to hear a bit more, but seems to be fine.
Papalymo: Too young.
Tataru: A tad high-pitched.
Alphinaud: Feels like it suits him well.
Alisaie: Very cute.
Merlwyb: Was unsure at first, but it's quickly grown on me.
Kan-E-Sanna: Quite good.
Raubahn: Pretty much what I expected.
Nanamo: Excellent.
My impressions might change as I hear more, but that's how it currently stands.