I recommend using Microsoft Word with Autoshapes. I've had a lot of success creating straight-forward diagrams for crew this way.
The "group" function is very useful. Once you're happy with the relative relationship between two objects (for example, the circle representing a chair and a rectangle that's a table next to it), select them both, right-click on the mouse and select "group". The two objects will then be manipulated together as a group. This way, if you add text above the diagram, you won't lose that perfect spacing between them. You can also angle them together, resize them together, etc. BUT the function still allows you to change an individual object within the group too. This becomes especially helpful if you have multiple diagrams within one document - no worries about updating one diagram and consequently having to re-do all the subsequent diagrams beneath it.
Play around with Word and Autoshapes a bit, and in no time, you'll be producing clean, easy-to-read diagrams.