I have been a winmo user for a very long time and I have to say that I love the option of being in total control of the UI. It's something I don't ever want to give up. Yeah the PRE, iPhone, DROID and others look cool and have some cool features, but the TP2 is SOOO easy to make it exactly how you want it. I can also get an app for just about everything that the iPhone can do. As for turn by turn nav, "amAze" and others work just fine for free. Another HUGE plus is being able to actually get into the registry and file explorer just like on a pc and change every little thing to my liking, like repeating notifications and everything!!
Oh and don't forget the option of being able to overclock the processor...
Winmo - hands down...