Have(had kinda) one of those large L shaped office desks(free from freecycle) that has a set of drawers that slide underneath the corner part, it's an old ikea model and the frame is designed for various tops, so i removed the metal part of the frame that bolts in to the support the corner (with an additional leg), marked up a straight line and jig sawed off the turn/corner part of the top, so it's just a long rectangular desk now (the metal frame and legs are central so it works either way around). I have the 3 drawer thing that would have previously slid under the corner/side part of the desk next to it and have the case on that alongside it. It sits about 14cm lower than the desk, but it's high enough i can see inside the window and the whole system, whilst taking no space up on the desk or on the floor where i'm liable to kick(i've tried under before) or bash into it with something, plus it's handily on wheels(so i can pull that sucker around or spin it if i need to get inside or plug something in).
I voted other, not quite desk or floor, but probably most similar to having it on the desk. Floor doesn't work for me if it's near me, i end up booting the thing, it can also get dusty at times and i have a super friendly cat that will rub up against it on the floor.
Before i hacked up the desk i did have the system on the desk, but now i've got less room, monitor arms and speakers with a sub, it's just not viable on there anymore and i'm not a fan of having it on the floor(for the reasons mentioned earlier).