I’m a fan of outdoor running. As soon as the weather’s reasonable (30s), I try to run outside instead of hitting the gym. I like the change of scenery and it gives me something to look at instead of a wall or someone’s sweaty butt.
But, not everyone likes the great outdoors: There’s wind, there are uneven surfaces and if you get hurt, you might find yourself far from your starting point.
Here’s an article that compares the two. It seems bit more pro-outdoors but it concludes by saying both will give you equal benefits in health. True.
If you’re planning on doing any races in the spring or summer, my advice is to spend more time outdoors running than on a treadmill. Race day conditions aren’t going to be as hospitable as the flat surface of a treadmill and the breeze-less gym. You might as well get used to it.
Besides that, who wants to do a long run on a treadmill if the weather’s nice and you can get outside? I’ve had to do some really long runs on a treadmill (sign up for a December marathon and you’ll know why) – it’s not the most fun.
What’s your preference?