I have a Schuberth C3 and a Caberg Sintesi. Had a Schubert C1 for a long time, saved my head (but not itself) when I was hit by a truck.
Both have an internal flip down sun visor, which I like. Neither sun visor is quite as dark as I'd like, though. My C3 came with a pinlock visor (the anti-fog device), but I don't like looking through extra layers of plastic so don't use it myself. I don't know if the Sintesi has pinlock as an option.
The C3 is very quiet. Shape is a little odd, and the sizing is a bit small, so I had to selectively mash the foam a small bit in a couple of spots to make it comfortable. But it is very comfortable now with excellent air circulation.
That being said, I like the Sintesi just as much. It flows air a bit better, in my opinion, and it fits great. It isn't quite as quiet. Can't tell any difference in the weight.
I switch between the two all the time and haven't been able to decide on a favorite. Also have a Shark full face, but I like the flip up style better.
Oh, neither my C3 nor my Sintesi are DOT stickered. Neither were sold in the US when I bought them; the C3 is available here now but it is very pricey. If there were still a material price difference, and I was buying just one, I'd go with the Sintesi.
G