Paste Without Formatting should be default
I'm running Geary 3.35.1.
Currently Ctrl+V invokes Paste (i.e. with formatting), and Shift+Ctrl+V invokes Paste Without Formatting.
In my opinion, it should be the other way around: Ctrl+V should invoke Paste Without Formatting. That's because in my experience, 99% of the time when I paste I want no formatting. I frequently copy text from web pages or other documents and paste it into a Geary message, and the formatting in the source document is almost never appropriate for the message I'm writing.