Having worked with both, IMHO 16mm still looks better than Digibeta, even on tape... a lot better if you actually pay to get a print made for theatrical screenings. Plus you get some experience of working with film, which is still going to be considered the 'professional' medium for movies for a few years to come, and it's probably a lot easier to blag a decent 16mm camera than for free than Digibeta. That said, I made a five minute short on 16mm a few years ago and by the time I had a finished print it had cost me several thousand pounds: so unless you're shooting with short ends in a wind-up Bolex and finishing it on video, 500 pounds won't go too far for a 15 minute short.