In order of speed from fastest to slowest for various conditions:

Flat: Tandem, me, wife
Climbing (including false flats): Me, tandem, wife
Descending (from straight to pretty technical): Tandem, me, wife
Descending extremely technical stuff: Me, tandem, wife
Momentum Rollers: Tandem, me, wife (tandem really cooks here, but requires HARD interval-esque efforts over the crests)
Italian (long) Rollers: Me, tandem, wife (these can really get to you on the tandem during a long series of them).