Not the best
I've had a look at MyTracks. The big issue for me is that, compared to nearly every other [sports] tracking app in the Android Market that I've looked at (e.g. Endomondo, RunKeeper, SportyPal Pro, Sports Track Live and [soon] Sports Tracker - the one that used to be Nokia Sports Tracker) it doesn't support the Polar Wearlink+ Bluetooth Heart Rate Monitor.
Apart from that, the displays look like they come from an Open Source app (which, of course, they do); no one has actually gone to the trouble of actually making the UI appealing.
You may be right about it being the best if it's really accurate, but I expect that's more down to the device it's running on than the app itself.