Unfortunately, I frequently have only one or two players, so the more experienced player has two characters and I have one as well. We only have household members, and that fluctuates, depending upon what kids we are fostering at the time.Assuming we are talking "non-DM players," I picked four. In my experience, that's the point where there are enough players to entertain each other, generate ideas and story material, and generally reduce the burden on the DM; but not so many players that it becomes a logistical nightmare to keep track of what they're all doing (both in and out of combat).
I'd say the next best number of players is five, and the next after that is three. Six is barely manageable. Anything less than three or more than six is right out.
Yeah, we ran a Masquerade campaign with 16 players one time. Two GMs, but it was still a slog and too chaotic for my taste. But the character interaction was very fun.My record is 16 players in a Night Below campaign. It was great fun, but combats could be a nightmare. I also had 12 for a 3e game of Gygax’s Necropolis.