Mine are in a mostly unused room. I use it as a "task" room kinda. I can pull out a folding table for sewing, crafts, whatever. The litter boxes are in the closet.
I had to vote "other". We used to have one in the upstairs hallway, and another in the cellar, but Jamie didn't use the "extra" one in the cellar, so now we just have the one upstairs. Our bathroom is really tiny, and the hallway has a parquet floor, so we put the litterbox there, right beside the door to the bathroom.
If need be, we'll put a second one in the downstairs hallway, or in a corner of the living room, as he ages.
The closet in my bedroom is empty except for the litterbox and container of litter. There's two litter boxes in the basement also. The one in the closet rarely gets used. I set it up when Cleo was ill and stayed in my bedroom all the time. I keep thinking I'm going to get rid of it and use the closet again, but I just never seem to get around to it.
One is in the spare bedroom, which I use as an office. It's in the corner next to a long bookcase. You can't see it when you first walk in the room.
The other is in the dining room (we never use it). I voted living room though because it's really the dining/living room (apartment). It's in the corner hidden next to a tall bookcase.
A box would not fit in our bathroom or kitchen, there's no way I'd stick one in our bedroom, we don't have a garage or laundry/utility room to put it in, no basement.
My dad & step-mom keep theirs in the kitchen, right by the door to the backyard. It's underneath the desk enclove thingy.
Know what would be cool to do if you were building a house? Have a built-in litter box area. Like a seperate room right off the laundry room or something, with a cat door to let cats in it but not dogs.
I voted other because we have six cats and eight boxes, so I couldn't pick just one.
We have four upstairs and four downstairs: of those, 2 are Litter Robots and one of each of those is on each floor.
Upstairs:
We have one in the guest bedroom - that's only for when Gary's mom stays with us. They like to sleep under the bed in there, so we didn't want anyone to get trapped in there when she closed the door for the night because she sleeps for like 12 hours. When she's here we put water and food in there too.
We have one in the upstairs hallway and two in the "cat room." (A third bedroom). One of those is a Litter Robot.
Downstairs:
The living room/dining room are one giant room (and we don't have a dining table - the eating area is in the kitchen). So we have two in there - kind of at each end of the room.
The other two are next to each other: one of those is the other Litter Robot. They're in the short hallway that goes to the powder room.
I voted "other". Our house has a "waterheater / utility" room off of the garage. When the house was built, we had them put a cat door between the office (off of the kitchen) to that room. It's the perfect place for a box...Cement floor and even an electrical outlet for when I get a LR.
One in the living room near the front door, since three of our cats are always itching to get outside to potty we figured placing it next to the door may be helpful.
One in the spare bathroom that we never use due to the leaking toilet (we've turned it off) and also keep a small 1 gallon fish tank with moss in there as a night light. No fishies though
And one on the enclosed porch which seems to have been completely ignored since we added the other two litter boxes in the house.