Vancouver, British Columbia
I teach the Geography of US and Canada four times a year. I enjoy teaching and learning about our nations so it is not tiresome or boring at all, but constantly challenging for a variety of reasons, not the least of which is finding our about how we are doing in re-creating the mess we have made of these great lands.
One of the questions that I am often asked in my classes is what is my favorite city. I do love New York, but I am from the west and so it is the western cities that most attract me, with Vancouver at the fore. On the water, ringed by mountains, much like my native LA, but Vancouver made very different choices. It is a clean New York with its highrise density and Canadian mentality. And don't let anyone tell you that Canada is the same as the US. It is not. You just have to spend some time in Canada for it to become obvious that here is a country that is peaking from under the shadow of its mighty, but tarnished, neighbor. I love Canada. I love the US too, but it is so full of itself that we have a long way to go before we finally "get it." Canada has been "getting" a lot of what the US has not, but it also is not perfect.
So, Vancouver. Why do I choose it? Let me count the ways.
1. The setting is beautiful.

A city on the water set against the Coastal Mountains is a place that is hard to beat aesthetically.
2. The compact living pattern that so many people in the city choose is the ideal for mass transit, something that most Americans will never see in the endless lack of community sprawl. Mass transit does not mean that you have no car, just that you use it when nothing else will do. When you live in a compact city where everything you need on a normal day is within easy reach, you don't need a car (and walking or riding a bike are much, much healthier for human bodies, let alone the mission GHGs put into the atmosphere). Mind you, traffic is still a bear in Vancouver, they chose roads over highways to avoid breaking up neighborhoods (do you have any idea how many neighborhoods in America have been lost when a highway took precedence over human habitations?)
Vancouver has multiple transit options. Car are still too important, largely because of a lack of freeways, but walking, trolleys (look at those overhead wires!) and the Skytrain offer other modes of getting around.
3. British Columbia is the home to any number of sustainable thinkers, David Suzuki being one of the most inspiring; and to ecocity ideas come to life: (International Centre for Sustainable cities; ; BCSustainable energyGreen Building sustainability ; 50% off the cost of a solar hot water system ; Laneway Homes (small houses built behind large houses to increase density and increase variety ; Using landfill methane gas to generate heat and electricity ; encouraging local foods and a sustainable food system)
4. The University of British Columbia. Enough said.
4. I have friends there. I met them on my Alaska ferry trip along the Aluetian chain. They were on their way to kayak around Unalaska. How cool is that? I have since visited them in Vancouver and enlarged by view of this beautiful city. Not perfect (any Vancouverian will tell you that) but way more sustainable than many places in the US.