It would be my 2006 koa / spruce GS, bought used and locally in 2010. It is my best guitar, period - satisfying tonally, visually, playability and comfort-wise. Second choice would be my all koa 2007 424 LTD.
I got to spend some time with the new 600's and 800's recently. They are very nice and will be "lifetime" guitars for many, but I already have mine. The newer offerings are appealing, but I'm all set.