I use nothing else right now to make up my g-code. Combining F-engrave, Paint and the features in Mach 3, you can do some very good looking projects. I have used Sketch-up but Paint is so much easier for the 2D drawings. I'm still looking for a free 2 1/2 or 3 D program to make casting patterns for small gas or steam engines, plus a myriad of other projects dancing in my brain. As long as I'm struggling with CAD drawings, I don't want to drop a lot of money on a program I'm not ready to use.
I wish there were some other features on F-engrave, like being able to use different fonts or type size in a single program. But, hey, it's free so I can cut and paste the code to make up what I want. I have to make sure to keep the original version because I usually mess it up a couple times.