Arids and Tundras
Arid and Tundra planets have the exact same statistics and therefore the differences are only cosmetic. They are average, beginner planets that have very little features but are used for their large amount of surface area.
Asteroids
Asteroids are not planets from a scientific standpoint, but can still be colonized in the game. They do not have much fertile soil and are therefore difficult to terraform (plant large expanses of greenery like jungles). Asteroids contain lots of crystals, however, making them ideal for crystal mining that will boost your colony's economy.
Crystalline
Crystalline planets are considered the most effective planets in the game for their abundance of crystals. The crystals can be mined by your colonists, boosting your economy and allowing you to purchase upgrades and structures.
Earthly and Gaia
Earthly and Gaia planets have high fertility ratings, meaning that they are easily terraformed. They also have an abundance of metal, which allows you to construct bases. The only difference between Gaia and Earthly planets is that Gaia planets have more surface area, allowing for larger bases.
Glacial
Glacial planets are ice worlds that are low on resources but have a high surface area rating, meaning you can build more bases. The Arid and Tundra planets have similar statistics, but have a higher abundance of metal than Glacial planets.
Magma and Volcanic
Magma and Volcanic planets have a low surface area and only an average amount of metal and average fertility area. They are known, however, for an abundance of gases which your colonists could also harness.
Metallic and Craters
Crater and Metallic planets have high metal ratings but low surface area. They are virtually identical, except Metallic planets have slightly more gaseous resources than Crater planets.
Oceanic
Oceanic planets have a high fertility rate but have a very low surface area to build upon and very little metal. The "Astro Empires" community considers Oceanic planets among the least useful types.
Radioactive and Toxic
Radioactive and Toxic planets have low fertility ratings because of their somewhat poisonous nature but have average metal ratings and are good sources of surface area and gaseous resources.
Rocky
Rocky planets have high metal and above average fertility and surface area ratings. This makes them ideal for ship building.