[snowwindwaves]

I use ladder only on Allen Bradley PLCs and then only for primarily boolean logic. the AB ladder editor is much better than their function block editor.

Generally I prefer function block, especially in Schneider's Unity, since I find it is easy to watch a process operate the way function block diagrams are animated. The function block also promotes code re-use by creating your own blocks.

I use structured text only when the problem can't be well represented in function block, or more like I haven't figured out how to well represent it in function block yet. It is much harder to observe the operation of ST as the tag values aren't animated. Of course you can't use breakpoints on a process without stopping it, which usually you don't want to.