At this point it is probably going to be a human rated Dream chaser. they were the 1st looser in the original commercial crew contract. They seem to be on track for a test launch later this year for Commercial Resupply.

Blue Origin is another company that talks a good game, but they've yet to put anything in orbit. If NASA is casting about for a second supplier, there were other rejected bidders on the current human space transport contracts (e.g., Sierra Space's Dream Chaser, still under development in a cargo variant) which seem less risky.