All things being equal, the smaller the home the less environmental impact it makes...from using less resources to build it, to consuming fewer resources to maintain, ie gas, electricity, etc. Also, check carefully the house's orientation to sun, wind etc. If you have a living room facing west and a huge picture window, that's a lot of heat coming in your home, no matter how well insulated and how good your windows are. Also, hard in newer subdivisions, good tree placement can cut your energy consumption. If buying new, and presumably taking a mortgage to do it, spend the extra and get the highest SEER air conditioning, energy-wise appliances, etc. you can afford. Then they are in your mortgage and can be paid off over a long time, you will break even long before their useful life ends (in most cases). Also, set up a regular maintenance schedule for your home. Clean filters regularly.....check seals and caulking around windows every April and october, for example. A lot easier to keep to with a new home, helps your resale value too!! Good luck.