You've watched most of the alternate century version, so there's really only the original gundam and it's many sequel left really. Disclaimer, I find most gundam to be merely okay show and pretty much just watched them for the mech (of those you watched I think seed is the best, IBO S1 was very good but S2 was a dumpster fire in a train wreck, 08th MS teams also very good, but it's very atypical for a gundam)
-If you want to watch the first gundam show, go with the movies, it had a lot of filler episode that get skipped in the movie.
-Zeta gundam is well regarded... but I find the main character the most insufferable POS in the history of anime, he's a character who make the world (and his life) worse whenever he take action. I could never get past the first 10 episodes because of that.
-ZZ gundam is sorta of a joke anime, if you didn't like fighter G, don't bother.
-Char counterattack is a movie, watch it for the sazabi and nu gundam (oh and it finish the main plot, but w/e).
-Stardust memory is pretty decent, it's heavily inspired by top gun, the mech design are really good, but it suffer from being a prequel of zeta that was made after zeta, so the event end in a bit of a wetfart ending and nothing that happen is really relevant.
-Unicorn is pure mech porn, amazing visual and action scene, terrible plot and actor. The main character isn't quite as bad as zeta MC, but oh boy does he try to be. The plot is complete non sense, with a big "twist" that's so stupid it hurt... but godamn! are the fight scene amazing, and the mech design good. Here's an example of the first fight (https://www.youtube.com/watch?v=mdrxmk-eiIQ) Stark jegan pilot forever! I'd recommend watching in japenes without subtitle, you still get the visual and can just imagine a plot that's not as stupid.
-Thunderbolt, technically in the universal century, but has little to nothing to do with the rest of them. Pretty good, although it tried to be too edgy for it's own good. Watch the first season, S2 finish on a cliffhanger that hasn't been resolved yet.
-Origin is a prequel to everything, don't watch unless you've watch most of the universal century stuff.
Otherwise there's a few other alternate universe.
-00 gundam is very similar in setup to wing, so you'll probably like it. S2 gets... weird and the movie even more so, I'd just watch S1.
-If you haven't watched seed destiny, skip at all cost. If you've watched it and enjoyed it, well you'll like zeta then.
-Turn A gundam is well liked, but it's essentially not a gundam show, it's much more similar to the old style of mech show, there's not really any politic stuff and only the main character as a mech.
-AGE is a kid show, it's mostly filler episode and isn't really interesting. It bombed pretty hardcore.
-Reconquista is G is a mess, there's something interesting in there but it makes so little sense that its hard to take seriously. For example, the first episode has the character riding in a space elevator with a bunch of cheerleader for no reason (both the cheerleader and space elevator), skip it.
-There's a bunch of build figther/diver stuff, just skip them, they're pointless stuff just to justify making new plastic model of older mech, and I say that as someone who love plastic model.
As for other mech show in the same vein.
-Code geass is probably the most gundam of the not gundam show, it's good but the writing get sloppy at time and the first half of S2 re-thread a lot of similar ground.
-I'd skip Aldnoah Zero, it start decent and the basic idea is cool (the main character are in the grunt suit fighting the bad guy in the super suit), but it just get worse from there, the MC is like an emotionless robot and the writting is piss poor.
-Patlabor is hard to get into, there's 3 version, the TV series, the OVA and the movie, all three stars the same character but are different universe of each others and re do a lot of stuff. Long story short, watch the movie (1 and 2) they're amazing if you like 90's movie (1 is a popcorn action show, 2 is a more of a political thriller), if you want more, watch the OVA.
-Eureka seven... Love everything about that show except the main character (never understood mech show fascination with incompetent piece of crap main character).
-Escaflowne is a shojo mech, it's actually really good and the soundtrack is amazing, it was sadly rush so the last half was compressed into a few episode.
-Macross is a very diverse franchise. Without getting into it, try frontier, if you like it for the Pop idol side, go with 7 and delta, if you like it for the action side, try the original. Oh and macross plus is a godamn classic, another great 90's movie.
