I'd like to point out that maps can basically be broken down into 3 parts: Points of Interest, Street & Geographical Labels, and Imagery.
Apple's Map's biggest complaints concern the first one, and the second one the a lesser extent. Most apps that use the mapping API are not concerned with Apple's database of Points of Interest, as they usually use their own data to populate the map. Imagery is the primary use of the API, so they are free to use Google, Bing, Apple, or anyone else, and they are more or less going to be equivalent at this level.
As Angst points out, the bigger concern is Apple not having a way of selecting the default action for parallel installed apps. Can't choose my map, email client, browser, dialer, etc. This is a valid concern, one that hopefully will be addressed in the future by Apple. Until then, people could use copy and paste. Hold down on the address in Contacts, select copy, then paste it into the search field of the map you want to use. Map app developers could make this easier as well. iOS has some pretty sophisticated data-type sniffers that can be used, and if it recognizes the data in the clipboard as an address, it could auto fill the field, further reducing steps needed by the user.