better had ~ had better: syntax

[Damien Hall]

Another comment on 'better had', as in

"Yo better had listen" = "It would be very advisable for you to listen"

Is this difference in word order a reflection of what I think is an American
tendency to be able to place adverbs before auxiliary verbs as a default,
unemphatic position?  In British English, adverbs can usually only be raised
that high for purposes of emphasis;  the raising will often be motivated by a
need for comparison, and will be accompanied by contrastive stress, as in

"New York buses are seldom red, but London buses always *have* been."

My intuition is that many, if not most, Americans would use the following as a
default version of that sentence:

"New York buses seldom are red, but London buses *always* have been."

A friend is doing some systematic work on this difference and is wondering
whether the different tendencies reflect different prescriptions, or simply
competing tendencies, where it so happens that one of the possibilities is
favoured in American English and the other in British, though both are in fact
available to both sets of speakers.

Any comments?

Thanks -

Damien Hall
University of Pennsylvania