This is always a tough one for me. I run my daycare on the main floor. I used to sleep a few upstairs (the younger ones ) and the older ones in the daycare room. The problem is that It really limited my own access to my home during quiet time. I couldn't watch my tv. I had to tip toe walking around etc. So, I"ve moved them all back upstairs. I sleep 2 together in one room and 2 in their own room.
In the fall I'll have 5 and the odd day this summer. So, on those summer days I will bring my big one down to the playroom... he'll be just about ready for quiet time vs. nap at that point anyways. And in the fall I'll have 2 under 2yrs and 3 over 2yrs. So, the 3 over will sleep in the same room and the 2 under will have their own room. .. I think... I'm still sorting all of that out.
My point is that it's important for me to have my own space at quiet time. I need to be able to do dishes without disrupting anyone. My husband needs to be able to come in and out of the house without worry of making too much noise. So, upstairs is my best solution. If I had a downstairs play area that's where they'd all be for sure!