I shopped these helmets yesterday but have reserved my decision pending additional "research." My impressions will naturally vary according to the individual, but for what it's worth:
Both are excellent quality, but I felt like the Schuberth was detailed marginally better. I have a pretty round head, and fit well in a Quantum 2, which is my standard at the moment. I am an XL in most helmets.
The Schuberth fit well at the cheeks but was a bit loose at the crown of my head. Not a lot, just enough to cause the helmet to ride down a bit if I jiggled my noggin. The chin bar felt like it would be too close as I lowered it, but once ensconced in the helmet it was just enough out of the way to work well. The sense of quiet isolation was superb. I couldn't really tell if the Schuberth pressure points would trouble me on a long ride, but in the store, apart from the slight looseness at the top of my head, it felt like it would be OK. I do not like the ratcheting chin strap, but I could get used to it; probably a result of familiarity after a lifetime of using D rings.
The Shoei fit a bit snugger for me all around without feeling uncomfortable. The Shoei is very well made, but the Schuberth's interior detailing seemed a bit plusher/nicer, more refined. It's fits at the chin bar (external) seem a little more precise (closer), though neither helmet rattled or felt insecure that way. I expect at speed the Shoei might whistle/make wind noise a bit more due to that though I have no way to compare in a static situation. The Shoei did provided much better noise isolation than my Arai in the store, but was not quite to the standards of the C3. It would still be a major improvement over my Quantum, I think. I felt that the "controls...visor action and locks were excellent on both, but somewhat preferred the Schuberth's incredible sense of quality. Both of these lids would take some getting used to; there's a lot going on with them once you add the visors and chin bar locks.
I liked the way the Schuberth looked a bit better without the space ranger spoiler detail of the Shoei, but that's not a deal breaker either way, and exterior finish on both is excellent. no ripples, perfect paint. I didn't notice a difference in weight between the two; again probably something it would take a ride to sort out.
In the end, I'll probably get a Shoei because proper fit is key, but if the Schuberth could be made to work without sliding forward on my head, I'd say it was just marginally superior. The slightly lower price of the Shoei is a minor incentive, and both helmets are pretty deluxe affairs. I could be happy with either as regards quality and design.