If you want to be the most green, a green condo is the most efficient way. They have a few of them up now, but given the rising cost of enegery they will soon be the norm. You save alot of energy being surrounded by people, but then you have to be surrounded by people so its a personal perference kind of thing. I prefer a house, but if you travel alot its way easier to have a condo. Houses are a lot of work!