The two things I really care about when it comes to picking a job, and one thing I care about a bit less. The two things that are very important are whether or not the class is fun to play (which is obviously subjective and I'd probably have to play them to really find out) and the aesthetic of the class (meaning both their gear and their animations). I also would prefer a more interesting job storyline but that's not as important as the other things.
Black Mage in terms of what I've seen looks pretty fun gameplay wise. Big numbers are always satisfying and it seems quite cyclical. I've heard that while their mobility isn't garbage they do want to move as little as possible, which isn't something I despise but I do like to be able to move around a little bit while in combat. Also the lack of utility is a bit of an annoyance (I get why they lack it, big dps) because I like having utility but it's nothing major. In terms of the gear, out of the three classes it's probably my least favorite because I'm just not big on staves but it definitely has some of the, if not the, coolest animations.
Summoner is the class I really know the least about gameplay wise. I've heard it's rotation is quite long and complicated which could either be fun or not, I'd probably have to play it to really find out. I've heard that having to move for them is less punishing then as Black Mage. Also, they do seem to have some utility (at least as rez) which is nice. In terms of aesthetic it's probably my favorite overall. Their gear is on par with black mage (except the horn thing, it might look good recolored but it looks stupid orange) but in terms of their weapon it's much better, I'm a sucker for spellcasters with books. Their animations are also up their with black mage, not their basic ones but the whole Bahamut orbital laser thing is.
Bard I've heard is reliant on procs to deal good DPS. I believe both off of other abilities for refulgent(?) arrow and their DoT damage for their gauge. I'm not really sure how I feel about that because on one hand not getting procs probably feels really crappy but procs make it a bit more engaging because it's not completely cyclical dealing damage. The three different songs you rotate between doing different things also seems pretty interesting. I believe they are able to be very mobile in combat though due to no casts time which I like, though it's not really that big of a deal. They also have some good utility afaik, though apparently they lost a lot going into Shadowbringers. In terms of their aesthetic, they have the weakest animations by far simply cause spells seem to have a lot more room for having great ones. In terms of their gear, I like their armor more compared to the other two, but I'd say bows fall somewhere between better than a staff and worse than a book for me.
I know nothing about their storylines since that be spoilers so I really don't know which has the best one. Thanks for any help deciding!