Lightning - not bad, not great either. I would say average, although Chapter 7 has emo moments with Hope, really pisses me off.
Snow - as somebody mentioned, dudebro. Stupid grin and restless energy.
Sazh - the best so far. The actor tried to making him sound mature (probably due to his age), and he succeeds. I know Satz is supposed to be a comedic relief in the JP version, but I like him in the English one. Very composed character.
Vanille - sexy accent
She is a bit too "yay!" and moe, but nothing too bad.
Fang - very little yet. From what I saw it seems she will be a good character, a bit like Satz.
Hope - die, die, die. HONESTLY! FFS, the amount of anime angst and emo is huge with Hope. First panic, then anger, then resignation, then some more emo moments. Then more emo moments in Chapter 7, really poor writing and he made Lightning feel bad as well. Need to ditch him when I get the chance.
So far Sazh wins hands down. Really like him as a character.