lucy24 - 8:05 pm on Jul 8, 2011 (gmt 0)
If you are a user and you remember-- or can guess at-- the site name well enough to type it in, would you be more likely to type it with or without the hyphen (not dash!)?
In English, hyphens tend to make words look improvised or old-fashioned. It may have a different emotive impact in German, since the language itself uses far fewer hyphens. They may even make the word look interesting or exotic.
If both versions are available, of course you would register both, so it's only a question of which one redirects to the other.