Image source: Apple.

While most investors know that the bulk of Apple's (AAPL -0.60%) revenue and growth during the last year came from its iPhone division, CEO Tim Cook played up Apple's services division prospects going forward, even releasing a supplemental filing with first-quarter results. The catch-all unit, where Apple reports iTunes, Apple Music, and App Store revenue, produced gains of 26% in the last year..

As a matter of general policy, Apple doesn't break down intradivision revenue any further. However, its the 2015 10K, Apple specifically addressed App Store revenue growth by reporting that it generated 29% year-on-year revenue growth. Apple's App Store competes with Alphabet's (GOOG -1.22%) (GOOGL -0.95%) Google Play store, as the latter boasts a considerable scale and reach advantage.

Since neither company reports specific app-based revenue figures, investors need to turn to third-party data providers for insight. When it comes to app research, analytics firm App Annie is perhaps the most-respected source on app-store market share. The firm recently published its 2015 Retrospective report, and it brings good news for Alphabet -- but better news for Apple.

Alphabet is king of downloads; Apple leads in monetization
When it comes to downloads, Alphabet has increased its lead over Apple. Last year, App Annie reported Alphabet had 60% more downloads than iOS. This year, the gap increased to 100%.

App Annie credited the tremendous demand increase in part to first-time smartphone owners in developing markets. The report credits Brazil, India, Indonesia, Turkey, and Mexico as the five countries responsible for nearly half of the company's year-on-year download growth.

On the other hand, Apple is winning the app battle where it counts: monetization. According to App Annie, Apple's App Store made 75% more than Alphabet's Google Play, up from 70% more last year. Earlier this month, App Annie reported Apple took in nearly $1 billion in App Store gaming revenue in just December, an 18% increase from the prior-year period. Per App Annie, Apple's monetization was credited to the United States, Japan, and China. The report finds 90% of the year-on-year revenue growth was attributable to these three geographies.

App Annie's data isn't perfect, but should be followed closely
App Annie's data, like most data, has limitations. Specifically, the company does not report Apple-specific app downloads like GarageBand and Keynote due to data-usage policies. Also, China is an acute conundrum for Android-based downloads. Technically, Alphabet's host of services -- including its app store -- are not allowed in the country. However, the open-source Android operating system (AOSP) is, and domestic forked third-party App stores are not included in App Annie's calculation, whether correctly or incorrectly.

More recently, it seems the battle for services in China is only going to increase. Reuters reports that Alphabet's Google Play, with both its digital-content library and app selection, will most likely be able to enter the Middle Kingdom this year to compete with Apple. Apple has recently been granted permission to roll out its iTunes store in the country, and Alphabet has been quite forthright about its ambitions to enter China..

Both companies have something to look forward to in 2016. Look for Apple to continue to monetize its App Store, and look for Google Play to continue its download dominance.

Editor's note: An earlier version of this article read “App Annie's data, like most data, has limitations. Specifically, the company is unable to track Apple-specific app downloads like GarageBand and Keynote.” It has been updated.