With girls your age, I would vote for Wishes. I've done both, and although you are much closer for the Illuminations cruise, you are kind of at ground zero so I didn't find the view to be as good. Also, if the breeze is blowing in the direction of your boat (as it was the night we did Illuminations cruise), the smoke is quite thick.
For Wishes, you get a fabulous view of the castle and all the fireworks. You may even catch a special showing of the Electric Water Pageant if your driver plans it right and docks you next to one of the Pirate Cruises (you might also want to consider this cruise with your little ones). We pulled up right next to a pirate cruise and got to see the EWP and also heard the Wishes music piped in from their boat.
Just some suggestions!