As a zoomer with better taste than my peers (not a high bar) this actually is shocking to me. I've put the Gundam Franchise in the 'too hard' pile for a long time, maybe it's time I figure out where to start.
Gundam, like everything Japanese, likes to retread the same ground, formula, and tropes - over and over again - but in its long history it has produced some good entries.
The heart of the franchise that I think captivated people is that the show is always asking: 'what is the role and obligation of obviously superior people?' And it will address it in different ways in each series, with the opposing factions representing the arguments and counter-arguments (with that typical 'no one is evil just because' + 'i have mixed feelings about this' nuance that the Nips always bring to the table.)
I'm not huge on Gundam, but I have excellent taste, and my brain is very very enormous, so I would recommend:
Turn A Gundam: the moon people want to (re)colonize Earth, and the show is mostly about trying to diplomatically solve a military occupation of the people who never left Earth - before it turns into a violent clusterfuck.
Mostly a political drama.
Any of the OGs that started the franchise: skip the first series if you have low tolerance for old animation. These are the 'space people are better than earth people, and want freedom/dominion, so they rebel.
What is moral?' Kind of stuff.
Iron-Blooded Orphans - a mercenary outfit seduces kids to pilot their mechs. they use an invasive surgery for faster piloting that tends to cripple said children. the kids eventually
take over the merc outfit and become their own thing in the solar system. This one is newer, a little more straight forward, a bit more flashy and stupid, and has more variety in vehicle design. A personal favourite, all though it's not very deep.
Child Soldier Shonen.
War in the Pocket: takes place on an orbital colony. A kind of 'the fighting has finally come to your city, and it's not as cool as you thought it would be' story. Told through the eyes of a kid who's about to get disillusioned.
Slice of Life: Warzone Edition