The RPHA 70 ST is the direct competitor to the Shoei GT-Air (dropdown visor, etc). I've got one of each (the original GT-Air, not the new GT-Air II). The Shoei's neck roll is really thick and plush and seals against your neck very well, so as I recall it is quieter than the RPHA. But it's not so much better that I would be willing to go without earplugs in the Shoei or anything like that.
The padding in the Shoei wins hands down, but I prefer the central placement of the main visor latch on the RPHA, and the slider for the dropdown visor is also easier to find on the RPHA. It's also quite a bit cheaper. Unfortunately, both helmets have a rather round internal shape and have never really fit my head very well.