I do most of my running on the TM. I have an overuse injury in my right knee that I just cannot seem to completely get rid of and TM is much more forgiving than ground. Also, I can set the TM at a slight incline, which the sports medicine doctor that I saw for my knee recommended. Finally, I do a lot of HIIT; it's much easier to push myself and track my progress for that on the TM.
When I'm able to however, I do like to run 6 miles outdoors once a week. I run on a dirt path that runs between a river and a lake. It's very scenic, lots of birds and trees, Mission Peak in the background. I have another route that is about 5 miles that runs through a state park and along the SF bay. It's also very scenic--on a good day I can see clear across the bay. That route is a little hilly through (and while uphill is good for my knee, when I'm outdoors what goes up must come down and downhill is very bad for my knee), so I prefer the other route.
I used to run from my house to the trail (I had a perfect 6 mile route all worked out from my front door). But with my knee injury, running on pavement or even asphalt is completely out of the question, so I can't do that route anymore. Now I get in my car and drive to the trail. Luckily it's not very far (especially since I've been known to lock my keys in the car and have to walk home

).