>>77866008Meme answers would be Decade and Zi-O but only because those are anniversary shows that show off the previous 10 years of Riders for each decade.
I'd say most Heisei era Riders(anything between Kuuga and Zi-O) are pretty solid picks though, some are weaker than other (Wizard and Ghost come to mind, Hibiki had a writer change halfway that made it very different, and some people didn't care for the romance aspect of Kiva), but they're all largely standalone shows so you don't HAVE to watch all of them.
I'd say if you want something "entry-level", I'd say Double or OOO is a good starting point. Drive itself is a pretty decent show in its own right.
And if you want grimdark, you have your choices of Ryuki/Faiz/Blade (known as the grimdark trio), Kabuto, or Gaim which is one Kronii listed as liking that's a bit more modern that involved Urobutchi so your mileage may vary there.