Settling on Mars isn't a simple as landing somewhere and putting a tent up, it's a big old place and some parts of it are better suited for habitation than others. The poles were once thought to be the prime Martian real estate due to the abundance of water ice in the caps, but Mars has seasons much like Earth, meaning that the poles would have midnight sun and eternal nights with the changing of the seasons. This would be like settling on Earth and deciding that the Arctic tundra was the best place to be. It might be a good idea, at least initially, to head for some kind of existing structure such as a cave or tunnel. Mars Odyssey found what appear to be natural caves near Arsia Mons, a volcano near the equator. These caves, thought to be the skylights of lava tubes, would protect settlers against fluctuations in temperature. Lava tubes extending deep below the surface would also afford complete protection from the damaging cosmic radiation that blasts the Martian surface. The question that remains then is whether its worth colonising a whole new planet just to go an live underground. Valles Marineris, not a Game of Throne character but the Martian version of the Grand Canyon that scores its way across the planet, is another contender. The canyon is vast at over 3000km long and an average of 8km deep, the atmospheric pressure at the bottom of the canyon would be up to 25% higher than the top - provided, of course, that it didn't fill up with water due to terraforming. Still not comparable to Earth's, and certainly not high enough to wander around in unprotected, but better than nothing.
