Running on: Asphalt
Pros. Since most races are run on the street, if you are training for a race you should get off the treadmill, so you will be more in tune with any obstacles in the streets. Also, running on the street can be better for those who experience Achilles tendonitis, since the sturdy surface keeps your Achilles tendon in a less-tensed position.
Cons. The road is made up of many different obstacles and dangers, from potholes to cars, which can make your running more unsafe.
Don't forget: When running on the road, always wear bright clothes and make sure you turn your music down low so you can be aware what's going on around you if you wear headphones.
Running on: Concrete
Pros. Running on the sidewalk can be the most convenient if you live in a city, and it also may be the safest option if you don't want to risk it on the road.
Cons. Concrete sidewalks are one of the hardest surfaces you can run on, which may translate to more stress on your joints and muscles. Most running experts recommend you try to limit your time on the sidewalk, but other studies have shown that there is no difference in the amount of stress on your body when you run on the sidewalk versus running on the road. But if you have injuries like ankle sprains or knee pain, it's probably best if you stay off the road.
Don't forget: If you want to run on concrete, make sure you have the best footwear for the job. Wear shoes with adequate cushioning if you find that running on concrete leads to joint pain.
So, which surface is best for regular runners? The answer: all of them. Depending on your body and your history of injuries, you should vary which surface you run on so you can work and strengthen different muscles and keep your body from adapting too much to one surface. This will help you stay injury-free. If you haven't varied your running surfaces in awhile, start slowly when you switch it up so you don't overexert yourself.