
Why you'd use it: CFEclipse is going on 6 years old now and has matured significantly.

There is no step debugging for ColdFusion. ColdFusion unit testing support is nonexistent in Dreamweaver. you won't be able to do it all in one place. So if you're a polyglot, or even just like to dabble in compiled languages (java, etc), then you'll need to keep another editor on hand for those tasks. For large projects, it simply does not have the code navigation features that many coders come to expect. While it provides for extensions, they're typically interface-focused (javascript validation, etc), unlike say Eclipse plugins, which can run the gamut. Why you wouldn't use it: It is not free, and it is certainly not a "coder's editor".
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All in all Dreamweaver is incredible software for web site designers.

It will do a fair amount of code generation for you as well (whether that code is "good" is debatable). It's pretty stable and, in my experience, hasn't been very "crashy". You can find a wealth of extensions, too. It can interrogate user-defined functions in the same page. It has good-enough code coloring and code completion for the built-in CF tags and functions. If you're a solo developer building a lot of "Tom's Corner Store" type of sites, even if they require some CF Coding (mailing list, subscribers, current specials, light content management, etc), its design tools, "template" features, and ease-of-deployment (ftp) make it an attractive choice. Why you would use it: its history as a designer tool makes it much easier for "non-coder" types to start cranking out websites.

There's rarely a "best IDE" for a language rather, there are multiple environments, each suiting particular needs. Just saying "use this, use that" is not at all helpful. I'd like to provide my personal reasoning behind why you might choose any of these editors (at least the ones I'm familiar with).
