Iksurfmag claims that Slingshot is the most popular brand for the year 2011.
www.iksurfmag.com/awards/readers-awards-2011/best-kitesurfing-brand-of-2011/

SBCkiteboarding says that Airush Litium was the best kite 2011.
http://www.sbckiteboard.com/2011-kite-review-display?news_id=1786

Don't know if these polls tell you so much... I guess that people in general vote for the kite that they are riding themself. But these polls should at least give us a hint of which kite that is the most globally sold kite :)

And here is a poll for 2012
kite2012.com/best-kite-2012/

Will be interesting to see the result by the end of 2012 :)