Portis- no Barlow- no Benson- no I would not be comfortable with any of them this week. If you cannot pick up a RB off the free agent list and you must use one of them, go with Barlow.
Maybe there are some less-known starters available. Ladell Betts? If no one is available I'd have to say Barlow because he'll get the goalline carries most likely (if we get down there) because of his size and Blaylocks lack thereof. Benson is a little nicked up, though he will probably be used too. I wouldn't go with Portis, after his injury I don't think they'll jeopardize having him reinjure it unless it's an emergency.