They all will work beautifully, but I like #4 the best.
#1 looks like Pac Man. #2 is my second favorite, but it's very directional. #3 is just a little too weird for my taste. I keep wondering the shape is - a question mark?
#4, on the other hand, reminds me of the rising (and setting) moon (and sun). I also see fans. It's very peaceful.
suschi