UMK3 is superior for these reasons:
Its somewhat more balanced then its Older Brother Base.
It has the ability to add an extra hit to a combo by jumping up in the air, press HP, and Then Quickly input the combo's standard motions.
The Whole MK2 Cast (Excluding Johnny cage and Raiden) is included.
Noob Saibot is no Longer Kano, Now that the Male Ninja sprites have been digitized.
And Lastly, 2vs2 and 8 Player tournament modes.
...Need I say more?