Well...if you are commuting 30 mins or so I'd say anyone of those bikes would do the job. There is nothing wrong with buying used. I ride old used bikes myself but I don't ride far and live in an urban area. My commute to work is 10-15 mins depending on traffic. The only reason I'd ride for 30 mins would be to get accross town for a social function or to just take a leisurely ride on the MUP. I don't need a high end road bike for my purposes.
Good luck with your commute!