Actually, I found the Song less annoying than the Cathedral ship. Mind you, I had overleveled Jr. and Chaos before then (they both have nice all enemy attacks)

KOSMOS is the best against Gnosis enemies,
Jr. against humans (though he's pretty good against anything)
Chaos against a group with different elemental weaknesses (due to his last ether spells)
Ziggy against machines
MOMO's the best healer (her attack in her normal form's almost useless)
Shion's more of a support character than outright attacker, though spell ray and her all lightning attack are quite useful. I transferred most of the healing ethers to her and KOSMOS, making a Shion, KOSMOS and Junior party quite deadly.