Draw.io is OK too, but the interaction is much slower when editing. The strict position/shape of arrows makes me want to clean things up way more than necessary and waste time.
I'd maybe consider miro or draw.io if I was working on something with other people and expected lots of edits and change history.
Mermaid is an interesting concept, but putting things in the reasonable location can be next to impossible and a single new connection can blow up the whole layout. And the integration is never quite polished - so many times I've been scrolling down a github page just to suddenly stop and resize a diagram. Then the panning/zoom is a bit clunky. (I know it's a client issue, but unless the defaults become reasonable, it's a mermaid issue too)