For Daniela and me, it depends on the situation. If one or both of us are getting together with play partners when time is tight we will get right to a quickie. The only requirement is mutual release.
When time permits, there is plenty of foreplay of all types. In those situations, foreplay may start for everyone with one partner, switch partners several times, then end up fucking with a person we haven't previously touched that session.
For me, the hottest foreplay isn't me doing anything with another partner, and it isn't seeing my wife giving oral, getting oral, or even fucking. It is watching another guy baring and playing with my wife's breasts. The only thing that comes close is Daniela DPing with two other men.