I stayed in Fiji previously... I’m pretty sure it doesn’t have any monorail views.While I will never say best. I would suggest Fiji Longhouse to be close the the GCH with some great "Standard" views of the Monorails. Next up would be the Rarotonga Longhouse, slightly farther away from the GCH but it does have a number of King bed rooms if you only have one small toddler.
Note: Second Floor rooms do not have a balcony.
Dave