Basically, if I'm playing with multiple players with different platforms, what platform do I choose when submitting my run?

whatever makes you happy :o)

both

any platform is good as long as u have W rizz

@spamshot83spamshot83 jokes on u i do

@HairDoMe1HairDoMe1 then why didnt u rizz me up yet

@spamshot W rizz

personally I would just do the majority and then add in the notes the multi-platform thing

Just choose the majority I'd say too