If you plan to ride less then once a month I say get the Mongoose if you plan mostly short road biking. Because it is cheaper. It should be a lot heavier though as Walmart bikes are made of heavier materials. The GT is probably the much better bike, and if you actually can mountain bike, and do where you live, it should be your choice. Mountain biking is really hard on inclines, and the probable extra weight of the Mongoose will make it a lot harder, and make it less likely you will enjoy it for basic recreation.