On my list of WP8 phones I want, the Ativ S is second place. I'm currently an Android user with my device being made by HTC and it's become clear to me how terrible they are. I was planning to replace this HTC phone with a GS3 but then I went back to looking into Windows Phone (I originally considered it when I switched to Android from iOS but the ecosystem just wasn't where I wanted it to be yet). But, my first information on the Ativ S made it the leader until I started looking more closely at the Lumia 920.
For me, the technology placed in the Ativ S is great but the Lumia 920 just has more stuff I want. I previously would have said that the micro SD on the Ativ would be huge for me but I've learned with an unlimited data plan and Google Play I just stream all my music so that I don't have to make sure all of my devices (I also have an Transformer Prime from Asus) have the same songs loaded onto them.
The Lumia 920 just has more things that appeal to me like super-sensitive touch and the qi wireless charging. Not to mention the Nokia suite of apps like City Lens and Nokia Music.
Although, were I to not pick up the 920 for some reason I would certainly be headed for the Ativ S. The rest of the WP8 devices (even the flagship 8X) just don't appeal to me nearly as much as the 920 or Ativ S.
So...I guess I'm saying I prefer Nokia but am not about to hate on the Ativ because Sammy makes some seriously quality devices.