Fixya, a website that aggregates fix-it requests for a variety of products, has examined the usability of mobile browsers and the results are worth a look for developers.
The company studied over 60,000 different help requests for the mobile browser category to determine which had the best "usability" and the answer was clear - Apple Safari for iOS.
Each of the browsers studied (Internet Explorer, Safari, Chrome, Opera and Android's stock browser) had their own pros and cons and Fixya goes into great detail about what they are. The Fixya report is definitely worth a look if you're developing apps and websites that will be seen in these browsers.