Visio brilliant for "drag and drop" functionality, but I now use Serif DrawPlus for just about everything, including plans.
It reads and writes PDF's which is a real bonus - I either ask for plans in pdf, or use Autodesk or similar (free viewer) to convert cad files to pdf, import into DrawPlus, drop my symbols on top, colour in a set for the zone plan, and output everything as PDF again.
Believe it or not my colleague uses Word for plans and swears by it - before you laugh, MS have nicked a lot of Visio functionality and hidden it in Word (2013 onwards) - once you add symbols to the library, turn on the grid and "drawing canvas", it isn;t actually too bad as a basic drawing program. The big advantage is that almost everyone has it already.
Matt