btop reports some gpu, network and disk information that I don't think shows up in htop, feels a bit more comprehensive maybe? Both are fine, but I too use btop, it's nice.
Random trivia: I think btop has been rewritten like 3-5 times now? It's sort of an inside joke to the point that someone suggested another rewrite from C++ to Rust ( https://github.com/aristocratos/btop/issues/5 ). I guess the guy just likes writing system monitoring console apps.
The new plasma-systemmonitor is garbage. The UI is very clunky, and it's missing a lot of sensors that were visible with its predecessor ksysguard, for example network sensors are entirely missing for a lot of people, and nobody knows how to fix it. I think it's beyond fixable to be honest, they should dump it and create something new.
For the time being I use ksysguard6, a port of the old ksysguard that's been fixed to work with plasma 6.