I find the Shoei to be better, in general, at least because of the shape of my head...
The Arai's are rounder-profiled, seemingly, so it takes me more turning to get a full rear-view sweep. With the narrower-profiled Shoei, the pillars (which run vertical next to your eyes) are closer to my eyes, allowing ME a more open field-of-vision.
The greatest suggestion here has already been written. Go try 'em on. Get the one which is best for you... And, since we're all different shape/sizes, all the advice you'll get, in the end, is merely subjective.
Good luck, yo!