When I try to dominate for a certain keyword phrase, I will use BOTH of the domain styles you've mentioned. After having done this in several niches, I can tell you from my experience that they will both rank well (assuming you build links, etc). In my opinion, there is no difference or benefit to one or the other. My biggest advice would be to get BOTH and really make a run at taking a few top 10 Google spots.
Hope that helps!