My absolute favorite thing to do in 5e is when I can find a niche spell that's perfect for a situation the party finds itself in.
This naturally draws itself to the prepared casters and especially the deep spell list and ritual casting of the wizard, but unfortunately wizard is also a generally good class which means there's usually someone looking to use it in a party, and while doubling up can be fun sometimes I like to have other options.
I'd like to ideally make something strong without any glaring weaknesses: I don't want to minmax utility off a cliff.
My front runner has been an arcana cleric, which enables Wish eventually and adds a handful of common wizard spells to its list, but I'm not sure the other features of arcana are all that great, and not getting heavy armor makes me a little leery of closing to melee for cleric staples like Spirit Guardians.
Any other cool setups that enable a lot of flexibility and utility?
I'm certainly not denying Bard's utility power, it's just not quite hitting the "oh there's a spell for that" feel I wanted out of this character.
I think we're kind of on the same page with this: bard can fill any role it wants very well, what I'm trying to do is fill a hundred weird niche scenarios. A bard can be a great skill monkey, blaster, controller, striker... whatever. you want.
But it can't really solve "we need to fortify this keep against a zombie horde that will arrive in a week", because the spells that would do that well aren't spells you can take for the other 99% of situations. A Druid preps Wall of Stone, Stone Shape, Plant Growth, Druid Grove, Move Earth, and Transmute Rock, and goes to town. A Bard might have one or two of those since some of them are actually pretty good for general use, but he won't be able to access all of them. And if for some reason he does, he won't have the toolkit for the next weird scenario that pops up.
Gotcha. In that case, I'd second Arcana cleric. Outside of that, you're not going to get something that does what a wizard does nearly as well.
However, since I'm throwing stuff out here, Artificer might pique your interest as a wizard-lite with a compromise of flexibility and non-flex. On the one hand, prepared caster, wizard-like list, but only half the amount of spell levels and slots. On the other hand infusions, which can only be swapped on level up, but can be given to anyone.
At lvl 11, spell storing also lets you expand spells with a target of "self" to your allies, or can be used to double-up on concentration by getting a non-magical ally to do it for you. That opens doors for simply doing more with with low spell level buffs. It is also used INT mod times per day.
Battle smith and armorer are technically the "better" classes because they can do frontlining. But for widened support, Alchemist adds healing that the wizard typically can't do and some random smaller buffs.
I'm very intrigued by artificer, and I think you're absolutely right: it has utility reminiscent of bard, but gets a prepared list that swaps like a cleric/druid (no having to worry about getting access to the spell), and a bunch of other utility through infusions. Filling your hideout with sentient plant spies through replicating Pots of Awakening is exactly the kind of stuff I'm looking for. The spell list is a little shallow to me, definitely not the same depth as the wizard list especially since it cuts off at 5th, but there are a decent number of niche tools there.
If there ends up being a good niche for a Defender or Scout, Armorer is on my shortlist, especially because it can plausibly fill both roles with the same build.