I can only speak for Ridgewood and surrounding communities.
While sq. footage is a factor, I would also strongly consider the comp homes SOLD [not for sale]. When viewing these comp homes look for similarities in location [busy or quiet street], new and updated kitchens and baths, lot sizes, style of home and proximaty to town, schools and commute. Your agent can furnish you with this info.
Again, in Ridgewood, we also use the tax assessed figure to arrive at a fair market value since we are assessed at 99.9% of CMV. [Current Market Value]. This is not the final word on value. Go will above first.
$prSqFt is an overused and misunderstood measure of value. Zillow and other sites have made it popular to consider, but itâ€™s not a reliable tool.
Consider that at the local grocery store one type of tomatoes may be 99cents a pound while another are $2.99. Both are tomatoes, but they aren't the same thing.
A luxury home of 5500 square feet with views and every conceivable upgrade may be cheaper per square foot than a 1300 square foot starter home that is very modest.
Use this tool when the comparable homes are in the same neighborhood, of the same vintage, built by the same or a comparable builder, but only use it as one factor.
As Anna indicated below, find a competent local agent who regularly tours homes, has meaningful experience in the neighborhoods you are considering to provide you with an accurate CMA on the home or homes you are considering.
There is no one most reliable tool, other than a reliable experienced agent.