OK here's the low down. I have ridden all three bikes. The America is the way to go in this comparo. I currently own an America and am willing to sell it. Only and I repeat only to get the new upsized bonnie cruiser that is in the works.
The honda shadow is a decent bike. It is underpowered though. It felt more like a 500 going down the road. It has good controls and they are easy to modulate.
The yamaha star 650 is not a bike for beginners. I say this because the clutch has no grab until the end of the stroke, the thing is just plain heavy, the steering is vague, it is underpowered worse than the honda ever thought about, and in general it handles like crap.
The america has good ergos, has good front end feel, handles well, makes way more power, and has more street cred. The switchgear in my opinion rival that of harley in their look. The others are square edged and look like they are straight from 1985. The america is the only way to go in a light weight cruiser.....except maybe for the new Kawi Vulcan 900 custom, but I haven't ridden one of those yet.
BTW, I have my America set up like a Speedmaster with risers, drag bars, and an SM seat.


06 BA, TOR's, 17T front sprocket, 135/42, needles shimmed, AI removed, drilled airbox, K&N air filter, desnorked, SM seat and risers, drag bars, pro-grips....let's ride!!