Given that they're essentially the same bike, just get the 6K. It'll save you $100that you can use for a light and a lock. I don't know a whole lot about these bikes but I wouldn't put a ton of confidence in either, in terms of long-term usability. For occasional riding either should be ok, but you may find they require a little more diligent maintenance to keep things working smoothly.

Get the 6K. Ride the hell out if it and if you love it, upgrade later to something nicer.