My Tracks or Every Tracks on Android work as a tracking programs, not as a route guides, AFAIK. I use My Tracks and it does autostop, and is excellent at tracking the ride to upload to Google MyMaps, which is how I use it.

I have as yet not gone the route of using a GPS route guiding program, mostly as on ANY smartphone, the display can be hard to read on a handlebar in sunlight, even though there are mounts for assorted phones should you want one. I did recently do a new route on Shelter Island, NY and had pre-traced the route on MyMaps, with the route map being accessible via a 3g cell internet connection and navigation on MyMaps, but in truth, it was a backup to a regular map in my back pocket.

Even with the stock battery in my HTC Incredible, I could track a 2 hr. ride using GPS and have plenty of battery left to last a 16 hr. day.

So it really comes down to what you want to do with the device, track routes, which Android app's do just fine, or route guidance, at which Garmin might be better if only due to better battery life over a long ride.

SB