Appcelerator conducted a survey on 2,363 developers in middle September regarding their opinions on the future and needs of mobile operating systems. Looking at the chart below, you can see that Apple's iOS scores better in more areas, but Android stands out in several areas, possibly most notably that 59% of the developers surveyed believe that Android has a better long-term outlook than iOS.
Appcelerator mention themselves that even thought the iPhone 4 has launched since they conducted their last survey, perception of Android as having a better long term outlook increased by over 10%.
Phandroid points out that the reasoning for this opinion lies with the number of devices poised to run Android in the future:
A full 72 percent of developers agree that “Android is best positioned to power a large number and variety of connected devices in the future.” Apple and iOS had the agreement of only 25 percent of developers. This means devices like Android tablets and Google TV could be a huge factor in the long-term success of Android as a development platform.
TalkAndroid echoed that belief, writing that the belief in the strong future of Android resides in the fact that "Android can be built into any device or platform by any manufacturer."
Appcelerator's survey indicates that 57% of developers feel Android has more capabilities and is a more open platform than iOS.
The survey also points out the shortfalls in the Android Market regarding layout, ease of discovering apps, and the perceived difficulty of making a profit. The survey also made note of developers' perception that Android is a more fragmented platform, and that Apple has the best devices.
Image from Phandroid