The answer changes from week to week. This week is the original Thump. Now that more and more companies are wanting to get into the wearable electronics game, I can appreciate more how ahead of its time the Thump was.
Last week, it was the OTT because of its display/artistic merit.
On another note, here's a thread with a Top 10 list:
http://o-review.com/forum_detail.php?ID=21&p=1
Things have changed considerably over the last 7 years.