Running - indoors or outdoors?

This morning, I completed my 3rd week of the couch-to-5k program. It was a lot easier than I thought it would be, and actually I kind of enjoyed it. There was a light rain most of the time, and that really cooled me off.

This led me to talk today about whether running outside is better or worse than running inside (on a treadmill).

My answer: neither! I think both have their advantages and disadvantages.

Outside (advantages)

• More scenery and interesting visuals
• More challenging
• Better preparation for a 5k
• It's Free!
  

Outside (disadvantages)

• Can be harder on the knees
• Temperature variations can cause discomfort
• More dangerous (cars, animals)
• Might be tough to find a flat area

Inside (advantages)

• Stable climate
• Don't need to carry things like water or an MP3 player
• Some treadmills have a calorie tracker/pressure monitor built in
• Can watch TV
• Lower impact
  

Inside (disadvantages)

• Can be boring
• Programming some treadmills for intervals is a nightmare
• If you don't have access to a treadmill, you need to buy one or join a gym

I prefer to run outside because I have a goal of finishing a 5k and because I don't own a treadmill. But that's just me.

What's your preference?