Best and simple Windows drawing program

So, a few questions:

1. Are you interested in 2D or 3D drawings?
2. Will the package be used to create 3D printing diagrams, i.e. must it produce .STL or AutoCAD files?

While you ponder these questions, I will tell you that I have been using Microsoft Visio for better than 20 years.  It has served me well in drawing floor plans, structures, and wiring diagrams.  I tend to make drawings of anything that I am going to scratch-build.  I then use the drawing to identify and size parts.  Visio is not free, but I find it very useful and worth the price.  It has a number of libraries with predefined shapes.

Here are a few examples of my drawings done with Visio.

The first is a top view of my transformer cart.

The second is a cross-section of the benchwork, subroadbed, scenery, and roadbed for a part of the 2-track mainline.

Finally, here's a look at a bench work table top.

I like Visio.  It's not hard to learn and has a number of great features and flexibility.  There is (was?) a free-ware version called Dia, but it lacks predefined shapes which makes it tedious to use.  I feel that Visio is worth the price.

George