Moai! is awesome! It's a great alternative to Corona and if performance is a problem you can always get into the source code and address it yourself.
I've personally contributed to Moai (upgraded Box2D to the latest version). Their team was quick to integrate the changes in addition to some bug fixes. They're moving really fast and it's getting better every day.
At first I was hesitant writing everything in Lua, so I took Moai for a spin by porting on of my existing games on iPhone B.I.T.S Pinball written with my own engine in C++. I was pleasantly surprised that not only was it almost just as performant but MUCH faster to re-implement and cut way down on the code. Lua coroutines are like magical pixie dust.
