If you want authoritative, you'll probably have to pay money. Accurate, current and authoritative information for things like this is hard to come by.
That said, you should not focus so much on testing it out with specific devices. The mobile segment is so fragmented that even if you manage to test it and get it working well with 50% of the devices, the other 50% are still uncharted territory.
My recommendation would be to take a representative sample of the Android and iOS smartphones that are reasonably still in use. For Android that typically means starting with Android 2.1 devices such as the Droid 2 (or even the original Droid) and scaling up to current-gen ICS phones such as the Razr Maxx. Repeat for the different vendors. Repeat for different screen resolutions.
You basically want to "modulate" (vary) the following variables:
1. Operating system (both version and platform, so e.g. iOS and Android, then Android 2.1, 2.2, 4.0, etc).
Screen size, from the smallest phones to the largest tablets.
Generation, from the latest reasonable generation still in use (depends largely on your customer base though) up through the stuff hitting the market in Q2 2012.
Network speed, if you're using network communications in your app... check out at least a 3G phone (e.g. EvDO) and a 4G phone (e.g. LTE).
As a corollary to network speed, you might also want to modulate on carrier, but you'll end up doing that anyway if you modulate the other parameters.
So if it were me, my strategy would be something like:
- Android
1a: Motorola
1a(i): Old/small phone: Droid 1 or Droid 2
1a(ii): Typical phone: Droid X or Droid Bionic
1a(iii): High-end phone: Razr Maxx
1a(iv): Motorola Xoom tablet
1b: HTC
1b(i): Old/small phone: Incredible
1b(ii): Typical phone: Thunderbolt
1b(iii): High-end phone: Jewel
1c: Samsung/Google
1c(i): Sidekick 4G
1c(ii): Galaxy S
1c(iii): Galaxy S3
1d: Lenovo
1d(i): ThinkPad Tablet Slate or IdeaPad (Android, not PC)
1e. Asus
1e(i): Asus Transformer tablet
1e(ii): Google/Asus Nexus 7 tablet
1f. Amazon
1f(i): Kindle Fire tablet
iOS / Apple: Just go through the various generations of iPhone, not many products to choose from...
Windows Phone
3a. HTC
3a(i): 7 Trophy
3a(ii): Radar
3a(iii): Titan II
3b. Samsung
3b(i): Omnia 7
3b(ii): Focus S
Obviously if you aren't targeting some of these platforms you don't have to test them at all. It really depends on what your requirements are and what your budget is. But these phones should provide a fairly representative sample.
Note that you will see much more variation in behavior and usability between devices on the same platform if you ship native apps. Web apps should perform relatively the same unless there have been major browser changes between versions of the platform. So all you'd really need to do for a web app is test it against the rendering engine of each platform at appropriate representative resolutions, and do as I mentioned with the network speed modulation.
