This is a personal choice but Latex in theory is perfect however in practice it's pain-in-the-arse. I'm using VS.NET HTML editor + raw HTML edit when I need it.
So I think using an WSIWYG HTML editor is best choice. You can always use a simple tool to convert it to PDF, and you can always edit HTML when you need something advanced. Also it's easier to put online when you need.
That's how I'm managing my software documentations and works fine for me.
