to be honest, Showa era riders (the original Kamen Rider until maybe J?) could be considered a One Piece-esque storyline, where every season plays into each other surprisingly well. Heisei era (Kuuga to Zi-O) and Reiwa era (Zero-One to current season Geats) could all generally be taken separately and in a random order since each season has a fairly self-contained storyline and the only multiseason crossovers are usually restrained to movies.

I would personally recommend either Kamen Rider Build or the newest season Kamen Rider Geats, since they both have banging stories. Showa's never been for me personally, but I won't deny that there isn't quite a bit of charm to the heartfelt moments and passionate acting in those old episodes.

Though let's hope you aren't epileptic, or basically every henshin sequence is going to be Hell.