My Tracks or Cardio Trainer?

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I have been trying to tweak the settings in My Tracks so that it will be reasonably accurate. Have seen a few tips here, but nothing helpful.

The problem is I can take the same route one day to the next, and be inaccurate by 1/4 mile or so.

Yesterday I went even further than prevous trips, yet My Tracks reported less distance.

1. Does anyone with experience with both My Tracks and Cardio Trainer have any data on which app is more accurate?

2. What settings are you using that yield the best (i.e. most accurate) result in the respective app?

Thanks!