Which Wiki text syntax or Markdown to use?

Working on my personal knowledge base... I want to format my documents, even on local hard disk in wiki syntax. Sometimes I would upload them to a (corporate) wiki, sometimes I would download them from there. Planned are some tools to support this flow and searching my knowledge base (documents) for later. Obviously I want the markdown to be compatible with most, minimising conversion work.

So my question is similar to this related question, but

• What wiki text version or Markdown (dialect) should I use when I start something new? (i.e. documentation project and kind of wiki).
• What are the most wiedely used/recognized ones?
• And where is tool support (editors and or libraries) best? Concerned prog. languages are Java, Ruby, Scala.

Wikipedia says that there is no commonly accepted standard wikitext language.

Creole is one effort for a "common wiki markup language to be used across different Wikis". There is a version 1.0 of the specification and several wikis and wiki engines implement it. MediaWiki does not implement it.

Markdown has a large number of implementations and seems to be used quite a lot.

As there is no agreed standard, the language might be selected depending on features and available implementations depending on the use case.