A simple analogy would be something like "Best browsed with the Firefox web browser" (boring) vs. "Get Firefox!" (catchy!) and although the latter says nothing about what Firefox actually is, it turns out to be much more effective over the first as a viral marketing tool.The problem is, without mentioning what Ren'Py is, people don't know why they should search for it. It's a chicken and egg problem, I think.
Well, here's how I think about it. If we say "Made with the Ren'Py Visual Novel Engine", when people see this phrase, they'll think, well this game was made with ren'py, which is just another VN engine like ONScripter or Blade.
But if we say something like "Powered by Ren'py", or some snazzy phrase like Firefox did, e.g. "Get Ren'py!" and throw in a cool looking logo, then when people see this they'll wonder, what is it? This scheme will be effective once they start seeing this catch phrase/logo in every game they play and every website they surf. When they finally click on the text/logo which leads them to the renpy website, they'll think... oh, renpy is a VN engine, everyone seems to be using it, its cool, its trendy and its in! I shoud use it too!
Anyhow, I'm not complaining about what phrase you're going to use, but I do think that "Made with the Ren'Py Visual Novel Engine" is kinda boring and can be improved on. Let me know if I'm making any sense in this discussion.
Oh, and it has been unofficially agreed on that the egg came first.