A recent report drawn up by Pfeiffer Consulting puts Apple, Google and Amazon's app stores head to head, comparing them with reference to various criteria such as the sophistication of their search options. Apple's App Store comes out on top, though arguably not by a resounding margin. But none of the three stores compare well to the theoretical target set by the report's authors: fundamentally, they criticise a lack of features such as natural language search in all three app stores.
The authors raise some interesting points, although the basis of their theoretical benchmarks isn't always clear. It's hard to imagine that a company such as Apple, with an app store that is now well beyond its teething stage, has not at least conducted a feasibility study on the inclusion of natural language search or that its programmers would be incapable of producing one. It seems more likely that the companies have decided that such a feature is not appropriate for app store searching on a mobile device.
Nonetheless, the report may be useful reading for those marketing cross-platform apps who aren't familiar with the discoverability features provided by all three stores.