The First 100 000 tiles sold in each country are Class 1. The next 200K (up to 300K) are class two. Following 300K (up to 600K) are class 3. And class 5 starting at a million.
Benefit of having class 1
Class one tiles are the first one bought in the country, which mean they are the cheapest, starting at E$0.1. It's also speculated that advertisement in class 1 will result in higher profit. The only country where you can buy new class 1 is Nauru. Many players sell class 1 tiles on the marketplace.
Why should I buy Class 2 or higher? They are expensive.
Firstly, you have no choice. If you want to buy new land, there's no more Class 1 left (except for Nauru). You can wait for a new country release, but last time it took seconds to sell all the Class 1 tiles. Second, it's rumored that more expensive tiles will produce more Essence. You can use essence to buy EPL, a private address.
Base classes are not in the game yet. Because the prices in the countries rise exponentially, the new players cannot afford land so easily. The developers are thinking about the Base class tiles which will be cheap.
What are the benefits of the base tiles?
They are cheap. Do you want to get creative with the Earth2 virtual land engine? You need land. Because the regular classes are expensive, you can purchase the base class. It won't yield any resources, but you can construct there. This way new players will be encouraged to join the game, they buy cheap properties, learn the game and maybe buy some expensive regular class tiles later.
Everytime someone buys a property in a country, the price for the country goes a little bit up. It starts slow, but later the increase gets significant.
Which countries are cheap
In the beginning, the players were buying tiles in popular places in the US, Germany, UK, Italy, or Korea. Many other countries were off the radar and that is why the developers of the megacities have picked them and bought land for their projects. Watch the Earth2 statistics to see where you can still buy the cheap new land. Link to statistics on the main page.
How do I know the class of the property
Before it's bough you can't see the class. You can however guess it (remember 0-100K is class 1, 100K-300K class 2 ...) and many sites offering Earth2 statistics suggest which class is currently sold in the country. When you open the details of existing properties, class is one piece of information you see.