Given these choices:
U+2010 ‐ HYPHEN
U+2011 ‑ NON-BREAKING HYPHEN
U+2012 ‒ FIGURE DASH
U+2013 – EN DASH
U+2014 — EM DASH
U+2015 ― HORIZONTAL BAR
U+2212 − MINUS SIGN
U+2E17 ⸗ DOUBLE OBLIQUE HYPHEN
The right answer is actually U+2015, whose alternate name is indeed “quotation dash”. Failing that, you are supposed to use U+2014. This is very common in Romance languages, BTW, using a quotation dash for speech quotes.
Note that even Bringhurst, who isn’t a fan of the long em dash, rightly says to use two of them for bibliographical entries. The recently released Unicode 6.1 has given us two more dashes to help with this:
U+2E3A ⸺ TWO-EM DASH
U+2E3B ⸻ THREE-EM DASH