On a poster, would 'We the commuter' or 'We the commuters' be more correct?
If you allow that something can have versions that are gradeable ("more correct") then it seems to be an opinion-based question. I've not heard of more correct, only correct and incorrect. If you're asking if "we the commuter" is incorrect, that depends on one's perspective. English allows for a lot of flexibility. It could be a play on words of "we the people" with commuter being used as a personification of the mass of commuters standing as one. Stranger things have been done with English. Think different.
- Commuter (noun, s.)
"As a regular commuter, I know the bus routes around here pretty well."
"I, the commuter, demand better services for my money."
- Commuters (noun, pl.)
"A train packed with commuters"
"We the commuters, feel that travel-services in the UK need to rethink their pricing policies."
Edit: I'm also tempted to suggest an apostrophe to indicate the possessive noun in Commuters' Protest.