Pen Tool!

The pen tool is awesome! This is fact! We all know this to be true! But why?
Let's compare it to a few other tools first.

Line tool
The pen tool can do what this does.

Shape tool

The pen tool can do what this does (in a more roundabout fashion, but it gets the job done).

Paintbrush tool
Guess what, it can do what this does too (once again, may take a bit longer, but it can do it). Not to mention you can create brushes with the pen tool.

Pencil tool
You know what to expect here, the pen tool can do it all.

So the pen tool can do the job of every other tool, some faster, some slower, but what really makes it special isn't that it can do the job of the other tools, but that it does the job of every tool combined! You can start a line, make a shape, trace something, and then make that into a brush if you want. And since it is vector based, if you make a mistake, just correct or delete the node! I'm not the most gifted artist, but when I discovered the pen tool (and vector drawing programs) I literally thought to myself, this is cheating.