for us we went with something more arty that didnt just focus on us but captured the moment and for our grandparents we went with something that we called "typical wedding photo". The two of us smiling sweetly looking straight into the camera
We had a similar thing with our engagement shoot. The picture FH and I chose (and adored) was very arty - black and white, off-centre, us in an underground tunnel, kinda grungy with graffiti and odd light. FH and I were facing each other, holding hands and kissing. We really liked the juxtaposition of the soft, intimate pose and the hard, industrial surroundings.
The whole shoot was more like that, which is very much our style.
My mother was appalled. The photo she chose? The colour one with FH and I sitting together on some steps, smiling straight at the camera. FH's parents chose the same one!
So try to keep your parent's taste in mind when choosing their portraits.