I don't know about bard, but technically (I've heard here) land druid (grass) with its haste and invinsibility is the most consistent. You can pick the warlock feat at level 4 and cast 4 eldritch blast/turn.
If you pick druid to then go warlock, you can also get away with a high charisma, low wisdom build I suppose. Thanks to thornwip and the AC on cantrip use boosting ring, land druid can also do melee.
A moon druid is strong playing tank in a caster party. Unfortunately, moon druids are bugged and not fully functional at the moment. Do not play that class If you're not a masochist. If you are a masochist, embrace the flaming sphere because you either need to give up on moonbeam or wildshape.
Flameblade is theoretically also an extremely powerful tool with that helmet giving an extra bonus action for fire damage spells. It's up to 36 damage a turn just from two bonus actions. Flameblade receives no damage penalty for being in your offhand, making it the best offhand weapon in patch 9. Flameblade also isn't boosted by strenght or dex.
Unfortunately (yet again), it's bugged and you lose concentration all the time. You can only summon it twice per long rest at level 4. That's two fights at best. Keep in mind Flame Blade also means no moonbeam. It's one or the other.
Being a Druid currently means either being an inferior Paladin (flameblade) or an inferior Tank (moon druid). Land druids can combine their powers to create unholy builds. Keep in mind even the mentioned 4x eldritch blast build means just being an inferior 4x fireball sorcerer.
There is nothing a druid can add to your party a different class can't do better. Consequently, you'll be playing the class for flavour and need a 3 man party that covers all skills. I'd suggest a battlemaster and then really just what works best with Lae'Zel and your particular Druid. If it's a Tank, you don't need shadowheart, If it's melee, you might want Astarion's ranged sneak attack, etc. You'll feel the gap.
When moon druid still worked, it was very fun to play a caster party in patch 8. With the recent damage loss and Druid wildshape down = Druid down, your druid will heal themselves or die. I'd pick a second custom Tav to go paladin so you're not dependent on Lae'Zel. Paladins can actually heal without using spell slots. Druids, infuriantingly, will waste their precious 2 Level 2 spell slots to get their hp back and be stuck with no damage options until long rest. Unless you want to hate that playthrough, get that back up Paladin. It's just better... In every single way. Especially the tiefling with a Smite as a bonus action and mass healing the party as a reaction (oath of the ancients).
