Soma is undisputed God. Highest DPS, best and most reliable healing, can take shortcuts, and most utility overall.
I would argue Shanoa comes in second for DPS.
Whipper snappers (John, Richter and Julius) and Fuma come next.
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Alucard is heavily situational. On the DLC bosses, he kind of sucks, since his weapons have no range, and he has to constantly be jumping to inflict any damage (Soma can just float).
Maria has arguably the worst DPS, but better mobility than Yoko and Charlotte.
Yoko is a step above Charlotte with better DPS, but like Charlotte, sucks once she runs out of MP. As such, she's limited to speed MP regen builds.
Charlotte sucks once she runs out of MP. Even though she has way more spells that Yoko, I would argue Yoko has the better overall spells.
All IMHO of course, from my experience playing the Xbox Live version for over a year.