It would be a mistake to leave, at great expense, a gigantic gravity trap like ours just to fall down yet another on another planet. Free Earth or solar orbit, or libration points among the planets, are the place to colonize.
Mars has limited room. Population growth would cover it in less than two centuries, not to mention suburbia syndrome, which would have the first settlers become real estate moguls selling to wealthy later arrivals who each want to buy ten thousand hectares of Martian land to build the equivalent of a ranch. Not only limited room, but immediately wasted room as they emulate the American property model. And they'd point guns at anyone taking "their" land, so don't picture a Star Trek utopia.
Free orbital spaces - rotating terraria - could be built out of asteroidal or lunar material ("rail gun" launched, using a recirculating bucket on a track to fling it into a manufacturing complex where abundant solar energy could power the industry. Build large structures (Babylon 5, tho I never saw the show) that rotate to create a down, air, containt whatever landscape or factory settings you want, grow their own crops, and house tens of thousands to who the hell knows how many once people figure out how to build BIG ones. In contrast to Mars, the environment would be compatible with humans. And so much asteroidal material is out there - even ONE could supply thousands of terraria - that we could house hundreds of billions. And point being, really - anyone who tried could go. Enough room for everyone. If Earth doesn't suit you, build one of your own. Mars, on the other hand, will be limited from the get-go. Not that I wouldn't go to Mars, to stay, one-way ticket, to live out my life. But I'd rather be part of a much bigger picture.
I noted Musk was going the wrong direction earlier this year. Can't blame him - NASA and the most vocal "crazy" scientists have been talking up Mars for sixty years. But I don't think he ever read "The High Frontier" or any of the 1975 Ames studies on space colonies (should be christened "terraria" - Kim Stanley Robinson takes the credit for that name, its perfect). He also doesn't understand that a electric launcher doesn't have to speed a rocket to escape velocity - just a few hundred miles an hour over a cliff would do to eliminate the need for a multistage rocket.
Focusing on Mars - or Luna (it ain't the Moon! It has a name! Lost cause I know) will waste another half century when we could be creating a far larger, and richer, and superior endeavor. And the industrial capacity of orbital settlements would be immense. Need an umbrella to shade the Earth? No problem, about ten years with downtime capacity on the terraria fabricators, and we have a parasol. Need ten million tons of titanium to build superrails or superhighways? Sure, splashdown where you want it. Earth needs to get the crushing industrial poisoning and overgrowth moved off planet. And it would be better, cheaper, and practically unlimited. We're grasping for oil when we are surrounded by enough energy to supply our civilization ten thousand times over just above the atmosphere. Poisoning our water supply for one last dreg of crude.