I would stick with the colon rather than a dash. Generally, a colon indicates that what follows is critical information, while a dash tends to imply that the following information is simply an addition and further explains what has already been stated. It's a matter of perception.
As for the ampersand, I would say it depends on a few things:
- Does the publication have or follow a style guide that dictates this
usage?
- What is the medium? I tend to disagree with one of the
comments on an answer above, that it should only be used in
Web-based media. In fact, I would say the exact opposite, because
space is rarely an issue in a fluid medium like a blog or e-zine.
In print, however, titles/headlines need to be short because space
is at a premium. Web media give you more freedom, and at that point
the question becomes stylistic more so than convention.