Every startup has this question to ask of someone. But, its not the answer to this question they are interested in, its a different question.
The question they want an answer to is, how to pick an android developer that will produce an android application that has high downloads? And it snot an independent question as it relies upon the startup understanding that they will have to allow the android developer to modify product features and functions to get to the point of having an application that is desirable.
Have you tried looking at their social quotient score? what the heck is that? Look at the views of their Youtube channel< mine is at close to 29,000, or their blog views, this one started late in 2012 so its still in bare thousands, or their stakcoverflow points score, mine is about 1500 not high but still in the top ten. The reason you are checking these sites is to see how they get an audience.
Why an audience? Mobile applications for the most part unless you are doing enterprise applications are impulse buys. That means you have to be skilled in getting an audience as if you can get an audience of thousands of members than you will get thousands of downloads.
A developer who is attuned to getting an audience will structure the design, look and feel, etc of a mobile application with specific audience in mind and they will even go to some lengths to analyze an audience to see what their desires, likes, and dislikes are. Just implementing a startup idea as a mobile application only will get you about 500 downloads a month, not any where close to a number that a potential seed capital Angel VC will fund.
Hold on, there is one more aspect of mobile applications. The way the ad model works on mobile applications is that if you implement a mobile application centered on a set of activities and allow the ad system to self select for that set of activities than those ads have high click through conversion rates as the mobile user views them as an extension of the application.
Sounds somewhat obvious and simple does it not?