I also am a registered user of PowerDigi, and it has practically saved me from throwing my TX out of a window.
PowerDigi is a program I'd recommend for any 320x480 device (that it supports).

I've been using a Motorola MPX220 for a while, it's a pretty good one; good for talking, decent as an older WinMo phone (can sync nicely, & can install apps, play media, etc...
Spec-wise I like the HTC TyTN II (no, it's not the ATT Tilt), it's coming to me in the mail now... The iMate Ultimate 9502 looks quite nice too, but it's not out yet, I believe.
I don't think i could be paid to use the iPhone since it would not work with any of my apps I already own, nor could it handle my media library.

Favorite? That's hard... For extended listening, I'd have to say Count of Monte Cristo, it's around 50 hours; Anything J. R. R. Tolkein, anything C. S. Lewis, anything Isaac Asimov... all told i have over 30 days of audiobooks....
Jeremie