the lightest one.(that fits)
for the price I'd go the mongoose, They're all getting to be old rims/spokes, cables,chains,brakepads, gumwall tires. you'll be in for more money to keep them going more than a year. For a beginner the the treks double isn't as good as the other 2 triple chainrings and with the downtube shifters will be harder to resell when you upgrade.