I don’t feel qualified to rank any countries as best, but I can offer anecdotal opinions. I know the Netherlands has had strong energy efficiency standards for many years, and the country’s small size forces them to be very efficient with land use. They’ve been doing very comprehensive town planning for a long time. They use a lot of wind energy. Germany also ranks pretty high for energy efficiency with getting a lot of electricity from solar and wind. You may have read about the small city there where car ownership is low and most people get around by bike and public transportation. Norway also gets a lot of energy from wind despite having large oil and gas reserves. They’re being smart and selling it to other countries to finance their clean energy future.
I know you’re asking “in architecture” and I’m not really looking at particular green-building techniques, but rather compact city forms, smaller homes which don’t take a lot to heat, and walkable environments.
Then you have the city-state Dubai, UAE which is known to have the highest per-person carbon footprint. Obviously they’re doing something very WRONG.
Abu Dhabi, UAE, is building the Masdar “eco-city” an interesting net-zero experiment, so that could go a long way in that country’s ranking.