Depends on which version of Sims I am playing. In Sims 4 I prefer households of 3-8 Sims because any less is very boring to me. When I start legacies, playing only one Sim in the beginning can be quite dull but it's made more entertaining by everything being so rough in the beginning. In Sims 3 my households tend to be a little smaller, usually 2-5 Sims because the open world means there's usually a lot to do and a lot going on, too many Sims can get overwhelming. In Sims 2 I still preferred larger households, but the Sims in that game were not as good at tending to their needs on their own, so you have to be a lot more diligent to prevent tragedies. In any of the games, if I have to play a household with only one or two Sims in it they tend to spend a lot of time away from home, just to prevent things from being very tedious.