Different apps suit different cases.
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iWeb: Waste of space.
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RapidWeaver: Good for newbies. I don't like the default templates and you have to pay for "add-ons". Probably the best option if you don't know how to do a website.
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Dreamweaver: Probably most professionals use it. It's the more complete but in my opinion is bloated. I don't like the interface and the generated code is not the best.
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Textmate: Powerful text editor. I believe it's the best (but it's not my favorite).
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Espresso: Seems like it has future but CODA is superior (by far) from now. I hope to see this app improve, specially if they incorporate CSSedit (they are the same creators).
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CODA: My favorite. The interface is great and the app is very powerful (complete).
For CSS:
CSSedit is the best (by unanimous decision). I use CODA for CSS though.