Space is extremely toxic for humans to live in. You can't grow food on the surface of Mars because of the lack of atmosphere and the lack of water. Colonizing space sounds more of a suicide mission than colonizing Antartica. I think colonizing Antartica is easier than colonizing any planet or moon besides earth.
1) An atmosphere that humans can breathe.
2) Relatively mild temperatures. The average temperature on Antarctica is 14 degrees Fareheight on the coast. The average temperature on the surface of Mars is -80 degrees Farenheight (What is the Temperature on Mars? | Space). Deviations from this temperature are also less on Antarctica than they are on Mars.
3) Proximity to the United States that Mars doesn't have
4) Ample supply of H20. We can get as much water as we need form Antartica. This is not true for Mars.
5) A supply of fish, penguins, and seals that can be used for food. Mars doesn't have this.
Because of these reasons, humanity should colonize and develop Antartica and humanity should build cities in Antartica before Humanity is to colonize another planet.