Last week, Robert Scoble asked whether anyone was doing a comparison of the online mapping services. He got a couple of capsule reviews in the comments, but I’m not aware of any major review.

Reviewing the “big four” in online maps — Google Maps, MapQuest, Yahoo! Maps and MSN MapPoint (yes, in that order) — is problematic: they rely on the same map data and routing engine for directions, according to Webmapper, so it basically comes down to the user interface and extra features layered on top. But that apparently makes a big difference; via Webmapper again, a report concludes that people believe Google Maps is more reliable because of its user interface. Presentation matters, in other words; data along isn’t enough. It may be that Google’s clean pages, lacking the cruft of other services whose ads drown out a comparatively small map window, matters more to the general user than the hackability and other virtues we, as map enthusiasts, focus on.

This excellent site compares Google Maps and MSN Virtual Earth by presenting them side by side, so that you can see how each of them presents a location at a glance. Scroll through one window, and the other window matches your move. The fact that each service’s API allows you to do this on your own page puts both of them well ahead of anyone else; Yahoo, for example, hosts the maps produced through its API. O’Reilly Radar puts them both well ahead of Yahoo and doesn’t even mention MapQuest.

Speaking of MapQuest, despite their total lack of buzz during the past few months of frenzied mapping activity, they still managed to lead Yahoo! Maps and MapPoint in traffic in June (though it looks like Google Maps wasn’t even measured). If my readership survey numbers are any indication — they’re coming, honest! — then Google Maps and MapQuest are roughly neck and neck, with Yahoo third and MapPoint far, far behind, or at least that was the case last April, before Virtual Earth entered the picture. Who knows what the situation will be in even a few months?