Usually Diazo although I consider Diazo meanwhile more and more as a major pain in projects than as a helpful solution:
- source and target markup and structure often different requiring complex transformations
- mixture of CSS selectors and XPath expressions often hard to read and understand, in particular after some time
- source templates often contain theme related classes that do not belong there. The markup of the source site should be in general agnostic of the theme markup but we often inject target css classes into source templates for convinience or other reasons. I also found the same issue in huge automative site that is based on Plone...very hard to maintain, very hard to understand for new developers in Plone what belongs where and why - in particular in legacy systems.
- we often fix things in Diazo that would perhaps better be fixed in source template because the source template are in some cases just broken
- Diazo rules are often to narrow or unspecific in order provide a certain flexibility to the backend developer without having to involve the frontend developer for every single change in the markup.
- Plone backend dev and frontend dev (Diazo) must work hand in hand and communicate. In reality there is no clear separation between frontend and backend devs - both need to work hand in hand.