Yes, Shadow FTW.
I'll jump on the "ShadowsTanksAreHardToPlay" boat for a minute and argue that if you master the hardest class, you'll have very little problems adapting to the "easier" classes.
Back to reality - Shadow is terribly easy to play. As is the enire game.
Yes, shadows are easy. But the tanking as a shadow is different, and that's why there are so many noobish shadows in this game. A shadow needs to wisely use his auto-heals and know the fight to pop the defensive CD at the right time.