Personally I find your basic Word/Google Docs to be just fine. As well as writing, I also do some lettering, and I remember I found Celtx a bit of a nuisance to pull the lettering from. Ideally you don't want to create any issues for your collaborators.I'm just curious what people use, software-wise, for writing comics.
I remember Celtx used to be an options. Not sure if it's still used today.