Visual Interdev's the one, macromedia ultradev tries to do everything for you and tends to fill up your code with pointless extra bits that make the code unefficient, the highlighting is also not to good.
Visual interdev highlights the code nicely has a knoledge of a good few of the objects, ie if you type "response." it will bring up a list of all it's parameters you can use. If you install the knowledge base aswell it has help on everything, it's the best one for VBScript