Simply:

What CAD software are you using and why?

Me:

For 2D

I use Solid Egde 2D Drafting  - free version

It's "free" (you need to register). I tried many of CAD programs, both free and full versions (including Autocad, Microstation, QCad, VariCAD.....) and this was only one intuitive enough for me to start drawing immediately without any tutorial.

For 3D

I use SketchUp, mainly for importing 2D files from Solid Edge. Again this was only software simple enough for me to start with. I tried full version of SolidEdge, after one tutorial for making 3D component I gave up to ever learn this on my own. Those proffesional 3D CADs have way of work something called history based modelling....? Maybe someone would explain this

For Schematics/PCB

For many years I work with Eagle. This is choice of many,  APM is done in this one.

Why? It is simple, supported, well workin, multiplatform and also has free version.

In my previous job I designed PCB in relatively unknow software Formica. It has some features much more usefull and more clever than Eagle, but has major drawbacks for our use.

Other support software for design work

Irfan viewer - basic image resize, crop, change file type.

Inkscape -  once used for drawing curves over scanned image

Gimp - used once for joining scanned pictures

Notepad++ - Must have text editor

Windows Paint - expensive, but really great bitmap editor :-D

Windows Snipping Tool - expensive, dead simple and useful