I think, note: think, not know, the biggest difference is that with dd it will clone the filesystem as well, making the flashdrive the same ISO 9660, read-only filesystem, thus read-only, while cp will read of the ISO’s filesystem and copy to whatever’s the destination filesystem, ex. ext4.
All of these methods work equally well - they write the data to the device. dd has the most complex syntax - and it was “recommended” on the Arch wiki until not too long ago.
… just kind of a habit - recommend was what has always been used and has worked well
cp and cat and all the other methods do just the same
dd is more versatile - but for this application (writing one complete file to some medium) this versatility is not needed nor is it used
Use what you like - I use cat instead of dd because of the simpler syntax and shorter command.
But then again - I do use ventoy to boot .iso files
and only need the cp command anyway with this