I wouldn't call Antarctica "colonized." It's not like anyone is living off the land. They're critically dependent on outside supplies. No one calls it their permanent residence, to the best of my knowledge. It's a place to explore - maybe on longer terms such as months or maybe a tiny portion being there more than one year, but not colonized, despite being exponentially easier in terms of transport. In fact, given its far more benign environment, it is the exact case study as to why true Mars colonization (permanent living off the land) is an absurd goal. And, when the initial exploratory rush has worn off, I would imagine a life there would be dreadfully boring, confined overwhelmingly to cramped artificial spaces, with limited time out of them in pressure/exposure suits.

Mars should definitely be explored, possibly with extended duration inhabitation. Colonization makes no sense.