have both phones, 710 and Omnia W. The Nokia handles whites better, white on the Omnia is a bit off, slightly blueish and cold. Conversely, the Omnia handles black considerably better and overall the screen looks sharper and brighter, just nicer.
The Omnia has very annoying volume buttons on the left hand side that I constantly press when holding it and this necessitates constant tinkering with the volume levels. Annoying. Likewise, the search button on the Omnia gets in the way when taking landscape pictures.
The Nokia, with its physical front buttons does not have this problem and the volume buttons are on the right side which is better for right handed people like myself. I think the camera on the 710 is quite decent, despite reading elsewhere that it is not. It takes far better flash shots than the Omnia W although in non-flash sitautions there is little difference in quality.
If I could swop the Lumia 710 screen for the Omnia W screen that would be great. I just about prefer the 710 as it is grippier to hold, I find the Samsung needs to be gripped in both hands for fear of dropping it, it' is a slippy little critter. Battery life is about the same for both.
Hope this helps