I just made the switch from a VX6800 to the Omnia. I like the Omnia so much better... and I loved my VX6800 passionately. I posed the same query as you last week. My thread is here:
http://forum.ppcgeeks.com/showthread.php?t=70502
As noted, the Omnia is thinner, lighter, has a bigger screen, better graphics, is aesthetically very pleasing, has tactile touch feedback, CC20 ROM enables GPS and the ability to flash to cooked ROMs, 5.0MP camera which takes great pictures, and on and on. I kept my VX6800 as a spare in case, God forbid, anything happen to my Omnia.
I've only owned my Omnia since late last week and I can tell you already, unequivocally, it's the best WinMo device I've ever owned. I was tempted to go with the Touch Pro also but this device is so much smaller and lighter. Even though you are giving up some RAM to the TP, it's still a very fast device, especially with a cooked ROM.
Can you tell I really like my Omnia?
edit: the *only* gripe I have with the Omnia is the proprietary connector. I mean, c'mon, give us a standard mini-USB connector.