Treadmill due to outdoor conditions. Don't like to run in the cold and rain. Also, because I'm recovering from shinsplints and the treadmill is softer.
Yeah, I'll run outdoors if its in the upper 40's, anything colder than that is un-enjoyable for me. And here in St. Louis we've had some colder weather as of late which has forced my hand to stick with the Insanity DVDs. We don't have a home treadmill any longer but we do have gym memberships. Which is where we are off to in a out half an hour.
Have you ever trail ran? I started that about 2 years ago and it's pretty cool. The change if terrain, the scenery....it's kind of relaxing actually even though its a bit more difficult running conditions.
Nothing gets your heart pumping like running down a winding, rocky path knowing you really can't stop if you wanted.