Personally, I think that today not exist so powerful and so simple editor, such as Source SDK (Or, to be more precise, VHE).
Although likely, it's all a matter of habit. Some people think that Blender or UDK is very simple and clear editors, though I have no idea how work with it.
Just keep using Source SDK, and one day you will realize how he is easy in comparison with other editors levels.

I was really into mapping when I learned how to work with Hammer Editor two or three years ago. Of course all these programs seem very complicated at first, but once you're trying everything out, watching tutorials on YouTube one at a time you will learn really much about mapping. For me the Sandbox Editor seems very complicated, however, I think this depends on which game you prefer and how much you really want to create content for it. Someday I'll learn Sandbox, too.

There's a new engine on the way and I guess it will have new tools.
I got the impression you couldn't make fully functional maps with Sketchup though, and you would ultimately need to use Hammer at some point, but maybe that's not true.

yep

I'm fairly certain that there is a tool somewhere in the SDK for converting Sketchup files into vmfs? I've heard about it before and actually attempted to use it but I'm- funnily enough- better at Hammer than Sketchup.

Is it a SketchUp plugin that goes to and from .vmf files? I think the plugin exports .vmf files at least.

https://developer.valvesoftware.com/wiki/SketchUp_to_Hammer_Export_plugin