Um, I do both sometimes.
Most of the time, I get to see the anime first and, if I fell in love with it, I'll look for the manga to read as well. This happened with, for instance, Rurouni Kenshin, Mushishi, Slam Dunk, Monster, Berserk, Blue Exorcist, Jujutsu Kaisen, One Piece.
I have come across a lot of good stories with the manga first but, for me, that's mostly the BL stuff, most of which doesn't get to be made into anime. My manga reading habit took not just time but space. I used to own hundreds of manga. Three years ago, I gave most of my collection away. I no longer buy physical manga but read them on official sites. Chainsaw Man is a manga series I started reading on viz.com last year. I finished it in a little over a week. And then I learned that MAPPA is making the anime. Can't wait. I wonder how closely they'll follow the original material because it's super violent. Currently I'm reading
PPPPPP which is a fairly new title. Love the theme of music, quirky art style and cast of eccentric characters.
Because the manga is the story creator's original vision, I'm always intrigued and want to read it. Twenty-plus years ago, Rurouni Kenshin was a huge hit. But the anime series stopped short of the final arc when it was cancelled after a lackluster anime-only filler arc failed to draw the fans back. This drove me to hunt down, buy and read the manga. Ten years ago, the first Rurouni Kenshin live action film was released. Last year, the last of the five movies tracing the entirety of Kenshin's story was released. (I watched on Netflix.) As a longtime fan, I'll say I'm finally sated and satisfied. The films surpassed my expectations. So my recommendation is, for Rurouni Kenshin, read the manga. Then watch the films. Kenshin is one of the most interesting and memorable story characters I've ever come across.
Over the years, I believe I see a growing reluctance to rely on filler material as an anime series waits for the mangaka to continue his work. Because nobody likes that. I'm happy to see more faithful adaptations. This is true in some cases even when the original material is not manga but light novels, for example, in the case of Eighty Six.
I'm sorry for the wall of text.