If you choose something else than illusion you will have 1 less feat that you can spend on something like (levitation,water breath, hell penalties, better checks for dex etc....)
Levitation: Took this one over Ability Check Feats because I think I will eventually fail maleb checks or something else and now I can use something better than levitation ring when maleb is near.
illusion: Paragon Spell Knowledge Illusion is nice because you will have 10 or so possums after that and you will just need p focus and p spell knowledge.
Illusory Army from that spell is still under testing but it's nice to have if you want to solo things and add up to(8 str tanks) to party. Illusory Army have water breathing but no levitation and +14 weapons. EDIT:there may be nerfbat coming soon so think twice before choosing this
conjuration: Time stop spell("The caster summons a phane, which freezes time for 4 rounds. The party is left out of the timestream, and is free to act. Bosses are frozen for only 2 rounds.") and whole party can move around while it's active. Very nice if used in combination like normal ts + wall bard ts + druid immutable (example for nessus fight).
You will also have 2 uses for spirit spell so you can use one from begin off every map and the other at the end of map.(Just an example)
necromancy: This is another nice option too. Does kd and even asmo will be kd'd. But does effect: (The party is made effectively ethereal, as by a Greater Sanctuary spell) to party members every time it's used and not sure if that's nice on every situation but still nice choice too.
Good spell when situations gets too tough and party need to get a way from enemies.
Enchantment: if you want some dmg there is option for that too Enchantment - Cacophony: If you have epic spell focus evocation or LL then Enchantment + evocation paragon mix might be interesting option too but hard to say.
I liked 10 possums, 2 spirits, army of 8 and ts over other spells.
Yes, you have to start out as a non-lawful alignment in order to level up as a bard. But you can change your alignment to lawful good in order to take the paladin level without any consequences to your bard abilities.