I know this would become a debate, haha. HAML has definitely disadvantages, ERB is indeed nicer if you need to write a lot of nested tags, or stuff like strong, small, etc. Still I've found it's more pleasant to work with... But that's just personal taste and I should probably make it optional.

Coffeescript is really nice, though it can sometimes be a pain to debug. Haml is more succinct than HTML and I like the forced tab alignment. The problem is I almost never write view code that does not need to immediately be debugged in the browser. So I have to pay a mental tax to transform it nearly every time I write it.

You can mix them.

    %p Here is a Haml paragraph with a <strong>bold</strong> word.

Personal preference, but I find haml infinitely more productive and easier to manage.