Benefits of the ATIV S over the 920:
- Removable battery
- MicroSD support
- 8.7mm vs. 10.7mm
- 4.8'' vs. 4.5'' (though this might be a wash for people concerned about PPI)
- Lighter weight (135 grams vs 185 grams)
- Bigger battery (2,300mAh vs. 2,000mAh - though this again could be a wash in terms of actual battery life due to the increased screen size)
Benefits of the 920 over the ATIV S:
- Nokia exclusive applications
- Super Sensitive Touch technology (able to use gloves)
- Higher screen PPI (332 vs. 306)
- Wireless charging
- Camera (this is subjective until the reviews are out, but with image stabilization on the 920 and the GS3 sensor being used on the ATIV, it's hard to see it not being better)
That's the unbiased list. There are arguments to be made for build quality (which would probably go in the 920's favor), though again, that is subjective. Another argument could be made that the support is there more on the Lumia devices, but we don't know what Samsung will do going forward.
Personally, I can't do a 10.7mm thick phone. If the Lumia was 9mm or 9.5mm I'd (possibly) chose it over the ATIV (still would prefer a 4.8''). But a whole 3mm thicker is a huge difference - keeping in mind the ATIV still isn't the thinnest phone out there, either. I'm a bit worried because I need to get a new phone within the next month or so for work, and if the ATIV isn't out I may have to jump platforms for a thinner phone. Would be a shame - I've been onboard since the OG Focus, have the Focus S, and was looking forward to the ATIV since it fit my specific needs. But thinness is a big deal to me, and the HTC 8X is only marginally thinner, plus I'd like at least a 4.5'' screen, so that tosses it out.
That being said, there's a lot to like about the 920. Nokia provides great support, they care about the platform, and they're offering some great technology.