Depends on how the builder set up the motor. Could have matched the port work to a set of pipes. IMO the T5's are what I'd run. Where you've got all three play with it and see what the bike likes.
Trust me, if you are really into riding a 4wheeler, you'll eventually get motor work done. The bug gets everyone. If the T5's give you more options, I would go with them.
Not trying to hijack the thread but thank for the props on the avatar!
Just do the right bolt ons: pipes, filter, timing plate, coolhead, and you shouldn't have a problem with that YFZ.
If this is just for shits and giggles I'll tell you what you should do. Advance timing, cool head, pipes of course (go with CPI's, but I'm bias) dune/play port and then just bore the stock carbs.