I'd say go sit on them both, or if you can bum a ride that would be even better. See which one feels more comfortable to you, where do you feel like you are sitting? On the Honda it was more like I am sitting in the bike, on the YFZ I felt like I was riding on top of it. The seat is a little harder on the Yam. The TRX is a better all around bike and a more comfy ride IMO. The YFZ is Faster out of the box but I think it is more at home on a MX track or the woods. Both can be easily made into ultimate dune quads for the right amount of $$$. It is all personal preference. Do you like Ford or Chevy? Is that more of the answer you were looking for?
Oh yeah, BTW it is a scientific fact that red is faster