Just skimmed through Bleach manga chapters.
The art is meh. Kind of plain.
Don't know why it's so popular.
One Piece is 100x better from what I've seen of the art.
Yeah, One Piece art is actually genuinely better than Bleach, at least on a technical level. Kubo barely draws backgrounds at all, his designs are very simplistic (sometimes he strikes gold but still), his panels are huge and uneventful, and he seems to only use hatching to slap huge flat shadows on characters or further half-ass the environments with overuse of speedlines.
Oda on the other hand will actually try to make his characters seem just a bit 3-dimensional and does good shadows whenever his panels aren't too tiny to notice detail on. His main problem is trying to pack too much stuff into his chapters so the anime can keep a 1:1 chapter-to-episode progression without huge amounts of filler. So his action scenes can be quite hard to follow at times. Also his female character designs... unless Oda creates a male character first and then genderbends it, they all look the ****** same!