When designing collapse and expandable rows, are there certain ways to choose between using a twisty icon vs a plus/minus icon?
Below are examples I've taken from google search ---
With a twisty icon:
With plus/minus icon:
I think plus/minus is better choice for a number of reasons:
But plus/minus looks a bit boring if not designed well similar to your second example. So design these in way that it looks apealing to users.
I think both are equally clear however I would never nest the twisty arrows. They feel more like a single level accordion so here are the questions I ask when deciding...
If there are multiple levels of hidden child items then use + and -
If there is only a single level of hidden items then either one acceptable
If I can click on the entire row to expand/collapse children then the twisty arrow is preferred
If I need the user to click the icon directly (to allow selection of text in the same row) then + and - is preferred
Since your examples show multiple levels of nested children and data that a user may need to select with a mouse drag then I would use a nice sized + and - squares that the user can click on to expand and collapse the child rows below it.