Would discount the Giant, as it's not a mountain bike, for the other 2, do you prefer red or green or orange, do you want 27.5 (current wheel size standard) or 29" (slightly older but still current standard) otherwise, and this goes for most bikes at the price range you looking at, they will be very similar equiped, probably with a Shimano Atlus groupset and Suntour forks.

One thing to think about with the forks, you can upgrade these to a higher spec via Suntour USA for a discounted rate if you want to improve these - SR Suntour North America