I love playing as Sophie so I have no problem with getting her skills up, I actually think she's the best A-artes fighter in the game, personally. Also there is that book of Striking that's good for Arte usage (but it costs an arm and a leg; I don't know how else to get the usage count to 9999 though, iirc there's an achievement or a title in that).
Pascal is high-risk and high-return, like you said her AI sucks donkey butt, but she's good in the player's hands (she also has what is probably one of the *best* Accel Mode skills....but the computer AI usually puts it in the LEAST effective spot to be of ANY use....).
On the contrary, I find Malik a really effective mage AI and he's fun to use as (for particularly long and brutal battles I love using him to support/cast with a title that helps out casting speed...omg, can you believe a MAGE is finally FUN to play as??!).
Hubert is a godsend, but he's probably the trickiest to use (along with Cheria to some extent; but as for her, she's a surprisingly "useful" fighter despite usually being delegated as the Team Healer). Hubert's Rolling Thunderbolt is probably the easiest skill in the game to spam.
Asbel is perfectly average in everyway, but I think his linked/altered artes are the most useful.
I really want to try to get all titles, but god....the game has SOOOO many [non-PS3-trophy] achievements that you need to accomplish. Also, stealing that old man's medicine in the arena can suck Evil Richard's hoity-toity ass.