Unity is free even if you sell games. The downside of course is the splash screen on boot, a whopping 4 seconds of "powered by Unity." I hate the term "powered by." As if my local radio station is "powered by Subway."
The upside of unity is the enormity of it. Unity now works well with 2d games which is nice. I've made a few games with GameMaker and Unity. I've even made a few non-game programs with Unity. I think the best thing to do is design your game, then go through each free offering and see if it can handle your ideas. The downside is that you need to learn some code to use it.
I'm pretty sure that you are out of luck finding one without a splash screen for free though. That's the only thing they get out of you for using the software for free. Worry about your game first, and then if it's every bit as awesome as you imagined it to be you can always buy the program afterwards to get rid of the advert. Unity has a rental program which I believe is $72/month. The others aren't expensive either for the pc only export.
In the spring I do plan on trying out Rpgmakervxace maker to make a very short playable book trailer for a book about a detective that my friend just had published recently.
The current game I'm making in Unity can be found in my signature.