What factors most affect the best git workflow for the job? Team size? Business goals? Tech choices? Personal preference?
I always start with GitHub Flow. I find this master/feature branch workflow to be the easiest to manage.
In the hundreds of repositories I've managed, Git Flow on a small handful - like 3. These are normally projects that either need to support multiple versions (e.g. v1.0, v2.0, etc) or the business is unable to release features as they are complete (e.g. works to hard deadlines).
I'd challenge the latter is usually not a Git issue, but a deployment issue. As such, you may still adopt a GitHub Flow workflow.