Table-tennis table: 乒乓球桌, 乒乓球台 or 乒乓球案子? I have found those translations of a "table-tennis table":


  乒乓球桌
  乒乓球台
  乒乓球案子


Searching for pictures of them, all 3 appear to be the same thing. On http://www.mdbg.net/ I only found 乒乓球台 .

Are those words interchangeable? Which is more commonly used?
All three terms refer to the same thing - table tennis table.

乒乓球桌 is a commonly used (1.58M results on Google, 2.60M results on Baidu) layman's term.

乒乓球台 is the technical term (both Baidu and Wikipedia use
 this term) and is commonly used (2.14M results on Google, 4.19M results on Baidu) as well.

乒乓球案子 is rarely used (0.21M results on Google, 0.13M results on Baidu) from my own personal experience.

When used by itself,

桌 refers to a table.

台 refers to a platform or a stage.

案子 refers to a long table or a plank used as a make-shift table.

If you are discussing about table tennis in general, you can also use 球桌 or 球台 to refer to the table.