Greetings!
Hmmm...I suppose I use many different types, really. I have developed my campaign world for over 14 years, and my world is roughly the size of Jupiter. That means that I have enormous seas, and numerous continents. It provides for lots of room to do many different things. In some ways, it's like a restaurant category. Depending on the area, there are different offerings. For example:
(1) In the Celtic Island group, the theme is more Celtic/Arthurian Myth. There are Fomorians, Humans, Faeries, Unicorns, Nymphs, Dire Animals, and such.
(2) Arathan: The most western part is a continuation of a Celtic/Faery Myth theme. The eastern area opens up more, and is demarked by a 2500 mile long mountain chain that is larger than the Himalayahs. The eastern slopes of these mountains, there are Chaos Beastmen, bizarre monsters, and Giants. Occasional Dragons can also be found.
(3) The Far North: Humans, Giants, Dragons, and Orcs.
(4) The South-East: Giants, Undead, Orcs, and Hobgoblins.
(5) The South: Humans, Giants, Undead, and different kinds of animal-people.
(6) The Far East: Undead, Humans, Yaun-Ti, Lizardmen, Tiger-men, and some Dragons.
There are others, but the dimensions are so vast, sometimes the players in one campaign, will never get out of one particular area, because of the opportunities and so on. Different campaigns have been centered or focused on different areas with different themes. Thus, there's a good deal of variety, and maximum flexibility. Yet, within the specific campaign area, there is a dominant theme that is maintained.
Semper Fidelis,
SHARK