Starter maps are my choice because they can be turned into any of the other things. Here are some examples:
An Island with a coral reef
A wood with a path leading to the outside world
A castle or even structure like Stonehenge
Some pirate ships in mid-battle
A fully furnished home
A utopian paradise
The scene from an iconic drama with useful loot hidden all over the place
A small airport or even a single large plane
Colourful patterns that could form a great base for adventures in Minecraft
Furthermore, starter maps can be more popular as everyone needs to spawn somewhere in Minecraft.
