It depends, I mean, with a young child, isn't quick transportation back and forth for naps a priority? From that perspective, the Polynesian and GF are the real choice.
Plus, I have to say, if you're there during evenings with Fireworks, you're not going to see a better show nor have a better view.
Our consideration would be the children, though. Think of your choice as "Do I want a 20-40 minute commute to the room when my child gets tired, or do I want to hop on the monorail and have them in bed in 5 minutes, just when they become 'Grumpy' (this is Disney, after all)".
I'd suggest the latter will yield greater peace of mind and overall serenity during your vacation.
Hey, it's win-win here, this is JMHO...