One way in which the quality of the traffic is measured, is related to which country the traffic originates from. This is rated in terms of Tier 1, 2 or 3 traffic. Tier 1 traffic (considered 'premium traffic') refers to English-speaking countries where the average population have credit cards and are used to purchasing online.
Tier 1 countries are USA, Canada, United Kingdom, Australia and New Zealand. This traffic typically is best for conversion to sales. Normally, this is the traffic you want unless you are specifically targeting other countries with your product.
Tier 2 consists of 44 countries that are rated 'good traffic' and are still viable for sales conversions, albeit normally at a lower rate.
Argentina, Aruba, Austria, Bahamas, Barbados, Belarus, Belgium, Belize, Bermuda, Brazil, British Virgin Islands, Costa Rica, Czech Republic, Denmark, Europe, Finland, France, Germany, Greece, Guam, Hong Kong, Hungary, Ireland, Israel, Italy, Japan, Mexico, Netherlands, Norway, Panama, Philippines, Poland, Portugal, Puerto Rico, Romania, Russian Federation, Serbia, Singapore, Spain, Sweden, Switzerland, Taiwan, Thailand and U.S. Virgin Islands