Hmm the original 1966 Ultraman I think decent way to start off. Introduces alot of elements that are still reconizable to this day.

Tiga is similar to Kuuga in which was a revival for the franchise and is widely popular for being very innovative and different style from the clsssic Showa.

Nexus is "dark" series but the mature themes are balanced by a very unique take on Ultraman and the show at the end of the day is telling you to not give up inspite of the darkness.

Mebius is an anniversary season with actors returning and storylines from past shows being brought up. Despite this Mebius anniversary elements in the 1st half is relatively restrained as such time is spent more on the new characters then the old. In fact I've met more people who got into Ultraman through Mebius then any other show.

Okay, great! I'll keep those in mind when I get around to starting the series. Thanks!

Max. It's a fantastic series, relatively modern, and it's a very traditional Ultra show that doesn't lean too much on references to older shows.

Like Kurona and Switchblade said, X and Max are good places to start, and since 2021 is also the 25th anniversary of the 1996 show Ultraman Tiga plus there is a high possibility the new 55th anniversary show this year is likely to pay tribute to it based on rumors, Ultraman Tiga would be another show worth checking out following these two. Ultraman Tiga is symbolic in that it is the 30th anniversary show but also the show that brought back the franchise after its hiatus following the end of Ultraman 80. And it is the first to introduce form changes, giving Tiga the ability to switch into three modes of combat including his default mode, thus giving him the name Tiga(pronounced Tee-gah) the Indonesian word for the number 3.
Personally though these shows I would like to say are recommendations if you prefer to start with something more modern yet have the most elements of a classic Ultraman show. After giving one of the previous recommendations a watch definitely give the original 1966 Ultraman a try.

I'm pretty sure we all figured this was happening, but it's nice to have confirmation: Chronicle Tiga & Z is getting a subbed simulcast like Z!

https://i.imgur.com/aWWxk6K.png

I'll be completely honest, I didn't think that this would get a subbed simulcast given it was a Ultra Chronicle series and is more a recap thing.

So this is a genuinely nice surprise.

Oh, neat. I wasn't sure about checking this out before, but this seems like a fine way to satiate my Ultraman fix for the next half year.

Just finished Return of Ultraman last week and I gotta say, out of all the Showa series I've seen so far (Q, Man, Seven, and now Jack), I think it's my favorite.

You've got some very memorable monsters throughout the entire show's run, the first ever legendary hero crossover, some gorgeous cinematography, Shozo Uehara's writing at the top of his game, and some really fun additions to the formula such as an emphasis on Hideki Go's life outside of MAT. Most episodes are briskly paced, and feature some stunning visual effects work that still holds up today.

What I love about it the most is how much of Ishiro Honda you can feel in it. As a Toho daikaiju fan, Return of Ultraman feels more like an extension of that golden era of the 60s than Toho's own Zone Fighter did just two years later. Even though Honda only directed 4 or 5 episodes, including the first two and the last episode, he set the tone by rooting the series in urban Japan and connected the series to a more urban, relatable snapshot of Japan than the more futuristic depictions seen in Ultraman and Ultra Seven. I think that more down to Earth approach made me appreciate this series more than its predecessors, which I also enjoy mind you.

Even though I know it's a wildly different series, I am eagerly anticipating finally watching Ultraman Ace (as soon as I finish Carranger).

After the success of Z, I'm assuming all future series will be put on YouTube. At least until Tsuburaya works out a deal with a global streaming service.

I mean this is probably one of the most genius moves Tsuburaya has ever made. Heck, it's a great way to see what people all over the world are saying and thinking of their product for a good focused 30 minutes. That's like 30 minutes of just raw and legit reactions and criticism. It would be stupid if they deprived people this venue and themselves.
In comparision, Toei I think needs to step their game up and learn a thing or two from the Tsuburaya playbook. It is great they are leaving the classics up indefinitely for fans, but I think they should REALLY consider doing what Tsuburaya does; start doing limited time streaming of current tokusatsu. Because honestly, it feels forced. Even their recent announcement of Kamen Rider shows finally being uploaded felt hardly exciting knowing that it is just old stuff.
But back to the topic at hand, I hope they keep on giving fans the current shows like they have recently done.

Just how many Ultraman comics have they made over the years!?

This isn't even the brunt of what I found cause I think I saw some issues by Viz which specifically mentioned the Ultra Brothers on the covers (no photos, unfortunately).