Have both the Titan and the Lumia 800. I think the Titan has a slight edge, but the screen and overall build quality on the Lumia is absolutely impeccable. Man how I'd love for a 4.7 inch ClearBlack AMOLED display. I love looking at the screen on the Lumia. It's just so bright and vibrant, and the blacks are just perfect.
I am pretty disappointed in the camera on the Lumia though. The Titan wins in that front by quite a large margin, and that's something I never would expect to say about an HTC phone.
If I could combine the best parts of both phones, it'd be perfect. I still think my Titan is going to be my primary phone though, and my Lumia will be my backup (or my "I don't feel like using the Titan today") phone.