The venue itself, the proximity of reflecting surfaces, etc., and what kind of photographs are desired will determine that for you. Who is the end user of the images and what do they want to see?
One style of shooting involves just on camera flash and it can be considered a style and it serves a purpose. The light fall off from the on camera flash helps isolate the subjects from the background, plus provides the light you need for a good exposure. This is the most common approach seen in society/celebrity shots at events.
Another approach, and one that I like if it can be set up, is to use a bounced flash from ceiling, or wall ceiling junction, for fill so that my on camera flash gives me 1 stop more light than the fill from the bounce. The lighting ratio between the subject and the fill will help emphasize the subject and, in combination with your framing and choice of DOF, will provide a context for the picture that the more common technique can't.
For celeb shots, the celebs are the subject and the only important subject. The visual context doesn't really matter. On camera flash is the most convenient and a very effective approach.
Other event shots, where the subjects aren't the only focus, are different. Here, people want a picture of themselves and the environment to show them as being somewhere. Your Joe Common and you've scored a ticket to something special. Which do you want, a great shot showing you, or a great shot showing you at something special?
Recommendation: A 800 ws strobe with a 7" reflector to bounce and a good TTL on camera flash, perhaps with a diffuser like one of the 'mini softboxes' for dedicated flashes. You won't need something like a Fong, or Stoffen, and they won't work as well as a dedicated bounce. They are most useful in a totally roaming situation.
Hope that helps a bit.
Vance
