There are some mayor differences between the Ninja and the HYO. First of all the Hyo is more expensive.. a couple hundred at the least. Offers inverted forks, dual disk brakes and is a FULL size bike. The frame Hyosung has made for Suzuki.. it's based upon the GS500 frame. You get more horse power (31 horse to the wheel) and the torque of a V-Twin.
On the other hand.. the Kawasaki always been a good 250cc. To bad that not much of the engine had changed. It's a bit faster on the top end than the Hyosung and obviously has the brand awareness which also counts for a lot.
I think that bigger riders fit better on a hyo as to were female riders probably be at home better on the Ninja.. You need to be about 5"4 to fit on the Hyo (unless you buy the lowered version)
All with all.. both great beginner bikes if you ask me!