Well Dreamweaver; mainly because it's the only designer I can find that works for the Mac. On the PC I have used software like Notepad++, PHP Designer, and PHP Edit; as well as Quanta Plus on Linux, but none of them really have the complete interface Dreamweaver does. No other software I've used has the software tree Dreamweaver does, which is really convenient and necessary to me. Few others highlight the code properly that Dreamweaver does, and the ones that do don't have a file tree.