So, what you are asking us is our opinion on which crappy bike should a big guy ride out of the three you've selected.....

With that said, forget the Gravity and the rear suspension at your weight. Cheap rear suspension combined with a heavier than average rider will only lead to disappointments. Stick to a hard tail for now until you build up endurance, drop weight and gain enthusiasm for a sport that you will spend more money on a better bike soon enough.

Value per dollar, I'd go with the Vilano, but only because it was on your list. Search Ebay and Craigslist for a better used bike than a cheaper new one.