Which diffuser/modifier for events/parties (for 580EXII)?

I don't normally do event photography so I'm not up on the best modifiers or diffusers for shooting people in party or event situations. I suppose it's similar to getting casual shots at weddings too.

Is the pull-out white reflecter effective on the 580EXII (flash pointed at ceiling, white reflected pulled out)? It seems like the easiest method, if it's effective.

Is it better to use the white slip on diffuser domes, which most people seem to use?

TIA
JJ