Out of my D&D groups, one has rotating GMs, with parties made up of:
6 PCs, 1 Cohort, and an Animal Companion (1 Familiar, 1 Partridge/Pear Tree)
6 PCs (1-2 Familiars)
6 PCs alone
The other group I DM for has a couple of different campaigns with:
4PCs, 1 Animal Companion
4PCs, 1 NPC
4 PCs, 2...