Last week Niall Kennedy published an informative comparison of different mapping APIs. He compared Google, Yahoo, and Live against each other. He compared the download size, the speed, documentation and the ease of use. Niall also looks at the specifics of each API. He notes that Google downloads more tiles than anyone else to prevent users from having to wait for the next tile. He attempted to use Mapquest as well, but found their documentation lacking. Open Street Map was not used due to a lack of US data — a known problem, their users (and thus data) are concentrated in Europe.
Niall’s focus was strictly on Map APIs. When choosing a provider it is worth considering if your app will need related APIs such as geocoding, traffic, routing and local search APIs; only having to worry about one API provider makes things easier. If you are looking for alternate Mapping solutions you can also try Modest Maps, Mapstraction or Open Layers; all of the open source frameworks have their advantages and all of them support the larger Mapping providers. You can find more resources on Mapping APIs at ProgrammableWeb’s new Mapping Portal.
In Niall’s comparison Google Maps comes out on subjective top. This isn’t too surprising given its dominance in mashups. Though Google’s was the first API people used to build mashups, the momentum could quickly decline if it became cumbersome to work on.