Most households land on biweekly, and there is a reason for that. Two weeks is roughly how long a well-cleaned home stays comfortable before dust, bathroom buildup, and kitchen grease become visible again.
Weekly makes sense when you have more than three people sharing the space, a shedding pet, or someone working from home full-time. Monthly works for smaller households, frequent travelers, and homes where most rooms go unused.
The other factor is what you want to stop doing yourself. If you are still vacuuming between visits, a shorter interval usually costs less than the time it takes back.