What would you recommend? What does the data says?
My audience is business and finance users as well as graduate students. Are there any other viable handset payment models that I should consider? Is there any good commentary or analysis available about the 3 choices?
Check legal. Depending what platform you talk of b and c may simply be illegal (the app vendor requiring all payments to be done via a.
If not a normal credit card processor may also be an option.
In addition to the regulations of the platform, which take precedence over everything else, you must consider the environment where the purchase is going to be made:
The goal of knowing this info is to adopt a payment system that has the least friction with the environment during the purchase process. Usually, decision friction arises from long checkout process and the actions that need to be taken outside of the device (e.g. pulling out the wallet).
In the case of in-app purchases, the native system is the obvious best choice from the point of view of user experience. Although it might be more expensive, this system reduces cart abandonment and provides greater customer satisfaction from the experience specifically due to its uninterruptible flow.
If you are developing for iOS, you have no choice but to use the native In App Purchase. Apple will not approve an app that uses a different method when it comes to digital content (nor will they allow physical content sold that via IAP).
If you are developing for Android, you will have a very hard time monetizing, depending on the country in which most of your users reside. The vast majority of android users do not have a Google checkout account and will not risk entering a credit card with all the viruses out there...
If you are looking for a credit card processor that works in mobile, I can recommend ZOOZ (we work with them, since we help app developers sell physical goods), but with digital goods, you have to sell via the monopolies.