Exercise logging with activity tracker

Hello everyone, I'm hoping someone can answer a question that's been confusing me. I recently received a Garmin Vivofit (1st Gen). I have not been using a HRM with it. I have been running 2.5-3 miles a day, 5-6 days a week. If I run on a treadmill there is a calorie counter on it, and if I run outside I use MapMyRun to log it. I sync the vivofit with MFP through Garmin Connect. Should I be logging those runs as exercises, though? I don't know if the "active calories" in Garmin Connect are including the runs. Today, for example, the treadmill said 446 calories burned while GC said 330 active calories burned. Should I log the 446 cardio? Should I leave them out all together? Does the Vivofit know the difference between running steps and walking steps and account for that calorie-wise? Any help would be much appreciated. Having all of these apps and gadgets is cool, but they're all kind of useless if the information isn't deciphered accurately. Thanks in advance!