I guess I'd better jump in here since we have one of each in our household.
Fly - pro's : I've notice it acclerates better and is more stable because of the larger wheels. It handles corners and curves really smooth. The top case is much nicer and better quality than what is out there for the LX150. It idles much smoother than my Lx. Any scoot in Dragon Red will go faster that any other colors
con's: Dh has acutally had two Fly's. The first one he traded in at 75 miles because it kept stalling out all the time, even when you were just cruising along. Last I heard, the dealer still could not figure out what was wrong with it and it had left many of their employees stranded somewhere. Dh had to have the dealer install a manuall fuel shut off on the second fly because it would flood very easily. Choice of colors, only 3 at this time that I know of.
Lx150 pro's: nice classic look and more color choices. Lots of accessories.
I have not had to install a manual fuel shut off on mine and I think I have only flooded it once. It rides a little lower than the Fly which is good for my size (5'5"). The pet carrier acutally comes out and makes for easier access to the engine . I thought it was very easy to change the oil on the 150 but I can't compare it to the Fly because Dh wouldn't let me change the oil on that one.
con's: not many. Top case isn't as nice. The acceleration and idle as mentioned above. Tires are not as sporty.
I also pretty muchagree with all the previous posts,( except for the one about the Fly being "bland")
test ride them both. You can't go wrong with either one, IMO. Really, the only reason I went with the Lx150 is I wanted a classic look and I love Daring Plum.