I think QT/Qtopia or some derivative like Opie is the way to go.
Why ?
Mature - QT2.3 has had many releases and hopefully Qtopia will finially be made compatable with QT 4.0 when it comes out.
Commerical Support - Has backing of a (Trolltech) company with professional developers. And Trolltech has been a very good citizen to the open community as well as the commercial.
Portable - Apps and libraries can easily be made suitable for the Linux and even Windows desktop as QT is the basis of KDE, and is also available for all other OS\'es. I like the fact that my shared data library is the same on the Zaurus as it is on the server as it really lets me reuse code, and provides more harmony from a developers perspective as I only have to have one API for handheld and server with respect to how the data gets sent and stored.
More then just widgets- QT has plenty of other nice tools that a new widget set may not even consider, like data serialization, and supports an external data format perfect for networks that PDA \'sa re now apart of. This means if you send a floating point you don\'t have to worry if the receiving machine is little endian or bigendia, QT does it for you.
Other tools, database hooks, File classes, FTP, HTML classes. and the list goes on and on. All of these let the user write one api regardless of the OS. And who knows perhaps QT will someday run on Windows CE or even Palm
I just don\'t see the reason for reinvent the wheel, when QT and Qtopia have a rather large critical mass in the Linux world. Why not just make it better by adding more funtionaily to Qtopia, and QT, much like what KDE has done. Like a better PIM or a embedded database.
Those are my thoughts. Hope my zeal for QT did not offend anyone.
By the way I love QT and Qtopia, but I hate the way Sharp has handled their libraries. and kept their code so static
-David