HTC Touch Diamond had a 4 gb cache, and Omnia came with 8 gb and 16gb.
At 16gb, Omnia was the same price as a 4 gb HTC Touch Diamond. Yes, I admit, Diamond has a far sleeker interface. The petite promoter couldn't stop emphasizing the silky smooth design of the Diamond. She told me Diamond had a weak battery though. I've read about the lousy battery life online as well, so I believed her. And I've seen pretty good reviews of Omnia's lasting battery.
So what do I like about Omnia?
First of all, I like the Opera browser. I like the streaming video player as well, as it allows me to watch youtube videos directly from the site. I've also used windows mobile before, so I'm familiar with the interface. I like the drag and drop style on the desktop, and the customizable widgets.
So, why the Omnia and not the iPhone?
Simple. Omnia has a longer battery life and it's removable as well. It also has a better camera than the iPhone. And it's cheaper too. I would also believe windows mobile supports a lot of applications.
So.. Omnia for the win!