Question is whether you really need markdown.
Dropbox Paper will save as .md which makes it slightly easier to get the note into Obsidian vault - if the vault is in Dropbox you can even save it directly.
But the key is probably what you find easiest for making the original note.
The main gain of a markdown app is that you have preview, if you are doing a lot of formatting.
Examples include Markor, Epsilon Notes, QuickEdit but there are many others.
I mostly don’t bother any more. I just do the note in Vivaldi (browser) which supports markdown syntax, then drag it into vault on desktop.
The key feature for me with the specialist markdown apps is whether they have quick access to the symbols I intend to use in a note, to save cycling through keyboard options.