Depends on the location I would say.
In America for example, almost everyone collects some type of US coinage (such as pennies, quarters, Morgan dollars), trying to get an issue per year and per mint.
In Greece on the other hand, collecting modern (after 1850-1900) coins (either drachmas or coins from the rest of the world) is the most popular form of collections. However, 2 Euro coin collections are also quite popular, especially with beginners.