I know what Gundam is, but I've never delved deep into the franchise so I'm not quite sure where to start or what to watch. The ones I've been recommended, and seen, are:
08 MS Team
War in the Pocket
Thunderbolt
And I already know to avoid Gundam Wing and that one where it's set in the future and Gundams are used in a fighting tournament or something.
FWIW I rewatched Wing back in either freshman year of college or senior year of highschool, years and years after watching as a kid either way and I thought it held up.
But I'll be honest the main draw for me is the aesthetic. I love how all the uniforms and mobile suits have this diesel-punky Inter-war period feel to 'em.