Quite a lot. I often enjoy both reading and watching, order doesn't typically matter, but there are a lot of anime adaptations that quite frankly aren't even worth bothering with if you enjoy reading.

And adaptations that go from anime to manga are completely beyond me. Why would would anyone read Kill La Kill?! So much of what makes that production such a masterpiece is only possible in the animated medium, a manga version cannot be an upgrade.

A big one IMO is One Piece. A lot of people will disagree, and there's always One Pace to watch a version that's a little more sane...

But all in all the anime is a massively frustrating experience due to how it has run for so long, with such inconsistent production quality and wildly varying pace.

In comparison, reading the manga from beginning to "current" chapter is a perfectly enjoyable experience. Obviously the manga has changed over the years as well, but it's been penned directly by Oda's vision, and simply tells the story of One Piece in a way that is... better, IMO.

I've been very impressed with the animation of the show in recent times, but I don't understand how the show is still using sfx and ost resources literally recorded back in the 90s. The animations and OPs/EDs have been updated... Yet these absolutely gorgeous animated sequences in these later episodes are utterly ruined for me by somehow sounding like they are still in 4:3.