I had to think a bit on this one because I think both are fun to jump in. The puddle is fun especially if you have someone to splash at like a sister who has a stick so far up her bu . . . never mind.
Anywho I like both. Water puddles are for splashing and making a mess. You can do a lot of damage with a puddle. They can be grimy and mucky with mud and that can really fuck up someone's day going to school if you splash them. If it's a cold day, then that's a big plus in the equation because the one you splash has to sit through early morning classes all wet, muddy and cold.
Leaf piles are great for hiding in and scaring the bejesus out of someone. You can run through leaf piles and disperse them while the dog chases you or you chase the dog. Fall back on great big fluffy leaf piles or make leaf angels. There are countless things you can do with leaf piles.