Atomic by far. It is SUPER basic if you want super basic. If you can download a file and understand how to click an executable, your golden. But, If you want to dive under the hood, This is where the real power comes in to play. There is not much it can't do. If you take the time to really look around you will keep finding little gizmos and gadgets that are everywhere. Really innovative stuff that I have not seen in other emulators. (and if you guys remember my silly rant while I was on the hunt for emu's I tried a LOT of them. )
LEDWizzard...Say no more.

Plus the layout editor. This thing is a killer. On the surface it may not look like much, but that is ok. The effort has been spent on making it a kick --I'm attempting to get by the auto-censor and should be beaten after I re-read the rules-- app. It is the Photoshop of the FE world. With total alpha control (for control freaks like me) and color based transparency, and overall object transparency you can make some wicked effects. If you use the trajectory settings you can make things move all over the place. I made a totally silly layout, just to test and I had stuff flying all over the place. Plus object scrolling and text scrolling and layer stacking manipulation (similar to photoshop) and text layout control and reflection settings with gradiated alpha (insert sound of Homer slobbering at a Duffs(or donut)) and background sounds for most actions.
And now, Plug ins...Yeeeeeaaah boyyyyeeeeeee.
Oh...and it runs MAME and a brazillion other emulators. (Funny that this has become the least talked about part of the FE arguments.)
I will write more, I have to go to work.