i have tried using omnibounce, reflector and a bounce card.
here is my experience on them.
reflector
produce very diffuse lighting. coverage can be a problem, depending on width of reflector. e.g. may not fill edges of 24mm lens.
good when there is no ceiling to bounce flash off.
bounce card - usually DIY, depending on type of material used, can yield pretty good results. can try laying crumbled aluminium foil on the card. yields pretty good results.
Problem with reflector and bounce card - when shooting vertical, have to reattach the reflector/bouncecard. this can be troublesome and time consuming (esp when things are moving fast).
this is where the omnibounce shines. can shoot vertically with ease.
Omni bounce gives pretty flattering light. i try to bounce it 45-60 degrees if in room with low ceiling. however, if in hall, then shooting straight with -1 stop off power still produces pretty decent results