I don’t do a lot of mileage and find it simpler to do a journal and fits better with my sense of logic (doing mileage doesn’t feel like supplier). As long as you put the details in and keep proper records I don’t think it matters which way if you’re happy with it. I guess if you had a staff member or more, then it would make sense to do supplier there, and therefore it might keep it all together to do yours there too.