Odin is pretty useless. It's not a bad idea to get him, but he really doesn't see any practical use.

Red Mage I would say is the preferred sub. Refresh for self as well as convert is nice. I basically never run out of MP anymore. While solo I have 3/tick refresh before refresh, 6/tick with refresh. Sch may have some uses for weather if your perpetuation set is really bad.

After 80 the bloodpact wards get some nice buffing.

Garuda's is great for movement speed.
Leviathan's is a pretty potent AoE attack down.
Shiva's is pretty potent AoE Evasion down.
Ifrit's is enfire that does ~43/hit at 99
Ramuh is AoE stun, it can last a really long time, it's really good
Titan is great, AoE buff Earthen armor, if something hits for 75% of life or more, damage is reduced by 45% (stacks with bard song, up to 95% total combined)
Carbuncle is AoE multiple status removal, useful at times
Fenrir ward is useless
Diabolos Ward is pretty bad. Low accuracy and expensive dispel