if in doubt watch it in release order but here's a good overview of the in-universe timelines (https://imgur.com/a/v5FNHoq) for a bit of orientation.

The shows outside of the UC timeline are their own thing, a lot of folks outside of Japan saw Wing first, those you can watch in whatever order you like. I'd say start with the universal timeline in order, it's the backbone of the Gundam universe. The shows between Mobile Suit Gundam and Zeta are side stories during the events of the original show but don't skip them (except for IGLOO) because they're straight up some of the best shows in the Gundam universe.

The "core" of Gundam is the original show, Zeta, ZZ and Char's Counterattack. Those in particular are one story and Zeta is widely considered (one of the) strongest Gundam shows.