Most people probably haven't had the opportunity to try a fixed-stem if that biases the poll. (though I feel most will vote that way) as far as functionality, a fixed stem is superior to the standard 3 piece gong setup.
If the diffusor is a 4-8 arm tree it will be much better than any diffusor. It might be a bitch to clean though.
the only fixed stem i've gotten to use is a BD that's got one small diffuser, kind of like an inline. i didn't really like that, it chugged a lot and didn't hit as well as a 3 piece. i'd love to get the opportunity to hit a nice fixed stem though