I came to AD from stage and film, so I use screenplay format. I like the readability and spacing, and actors are already familiar with the format. BBC had a radio play format that is pretty nice, too. But I’m stuck on screenplay.
One thing I find helpful is to keep everything electronic. THat way if I work with someone who likes a different format, it can be easily converted in most writing software, like WriterDuet/WriterSolo. Celtx, and Final Draft