What Showa rider would you recommend?
 

I've watched a bunch of Heisei and a few of Reiwa but never finished a Showa rider.

Try the 90s trilogy of movies, which is easier than the whole show. Also Black is very good, Showa at its best. You can also try Amazon with its ultraviolence:
https://i.ibb.co/BV9nBvR4/Amazon-Blood.jpg

Black. It's still very Showa, so you're going to be looking at mostly one-and-done stories about the latest Gorgom plot with the occasional interruption for a major plot development. It does end with a more serialized arc, though, that gets very, very good.

Kotaro is a good lead character, the recurring villains are all great, and the music is some of the best in the entire franchise. Importantly, the production quality is much higher than the older shows, so it doesn't have that really dated look that makes the 70s and early 80s shows a more acquired taste. The action is really good, but do be aware that there are a lot of flashing lights with Black's finishing moves and they will absolutely be a bad time if you're photosensitive.

Black RX is also a good choice, but it starts off a lot sillier and that can be a deal breaker for some people. It gets really good around the late teens, though, and if you're more into Kamen Riders with form changes you might find that more appealing than Black.

I'll second Mesnick's suggestion of Amazon. Also watch V3!

It's difficult because all of them eventually, and by eventually I mean starting with episode 3, devolve into exclusively weekly plots at which point it all depends on which gimmicks you want to see repeated 45+ times.

I'd say start with Black because that's objectively the best one and among the newels of the bunch so suit-design and special effects are noticeably well done.

If you really want to go old-school I would recommend Stronger, it’s been ages since I saw it but I remember the rogues gallery being fun, Tackle was cool and that I generally had a good time from start to finish.

Super-1 also left a strong impression on me, but for the wrong reason, the first half is amazing but the second one a complete disappointment.

Objectively how, exactly? Like best ratings or merchandise sales?

Agreed. I'll add another vote for Stronger.

Super-1 is incredibly fun all the way through. Definitely recommend that one.

That is probably the case given that they felt a sequel was in order, but I just meant an objective look at production value, set-pieces, special effects, storylines, characters etc.

It’s objectively better than everything else in Showa. Doesn’t mean everyone is guaranteed to enjoy it the most but still.

One can proudly have Kamen Rider Black join the likes of Superman and James Bond without any issue. And I’m not saying that because I feel like that would be the case, I’m saying that because it happened this very week ;) :lol

https://i.imgur.com/BioiwYH.jpeg

Fair point if general production value is better than what came before, which is likely considering it aired in the late 80s, although I'll contend that storylines and characters are subjective elements. For another example I'm more familiar with, Zi-O is the "best" Heisei Rider, but also a polarizing one.

They're all worth a watch, but my must-see Showa shows are:

Kamen Rider
Kamen Rider V3
Kamen Rider BLACK