The IBM web site contains an article by Mikko Kontio comparing six mobile development technologies. He makes a brave effort of comparing SMS/MMS, MIDP, Symbian, Pocket PC, Smartphone, and Palm OS.
I find that the most important factor, not featured in the article, is whether what you want to do is actually possible under each technology. People often come to me with a chosen technology well before they know it’s even possible. For example, many people come to me with ideas for J2ME applications that require access to the phone’s internal APIs. Similarly, it’s common for people also think they can change the user interface of the Series 60 built in applications.