Today's world is integrated and a good mapping software enhances this integration. Any new buyer going to buy a phone lists Maps as an important aspect while buying a new smart phone.
On the scale of 10, maps rate about 4 to 5 for being a pre-requisite add on. But recent stories about Apples IOS sending users to forest, it is important to compare the maps available on various smart phones.
Android: Google Maps (Developed by Google themselves)
Blackberry: 3rd Party Software
iOS: Proprietary Maps developed by Apple
Windows Phone 7 & 8: Nokia Drive
Nokia Symbian Phones: Nokia Maps
Bada: Samsung LBS (Route 66)
WebOS: Carrier Software developed by HP
Out of this I have used Google Maps, Nokia Maps and Nokia Drive and in my opinion Nokia Drive is the best Map available. Google is good but at times it is scratchy and hard on old phones. Nokia is a clear winner in mapping software.
I have not used iOS maps but have heard they are worst. Give your comments on the best maps you have used. At Least we will know where on earth we are on this front.