Haven't kept with Ultra since Ginga S (which I didn't really like).
I'd say Nexus and Mebius are my favs so far and I really want to rewatch them at some point.
I've seen Tiga, Dyna and Gaia quite a long time ago and don't remember much about them (my strongest memory of Gaia is Ultraman Agul theme).
Ultra Galaxy was pretty neat, wish Tsuburaya would do similar things more often.
Zero Movies were enjoyable, even if only the first one captured sense of fun and scale of Ultra crossovers properly. I still don't understand why Mamoru Miyano isn't playing Zero's host somewhere. You'd think he at least tries it once or something and I remember some rumors about it flowing around, but nope.
Initially disliked first Ginga series, but in retsospective I see what show might have tried to be (sort of a small-scaled side story to much bigger events all over Ultraman universe). I still don't think this show works for various reasons (like the main villian).
Also, I'm not really feeling "transform into past whoever" gimmick at all. Why aren't these new Ultramen carving their own identity? Ginga has like 8 forms on top of his ability to use Spark Dolls.