One-all.
But in terms of overall bias, there's nothing in it. While I'll listen to a variety of artists and a range of genres there's nothing that predisposes things one way or the other.
Making that decision could come down to whether you anticipate your future listening habits as based on what’s gone on in the past or focussing on what you’re going to be listening to in the future.
In terms of the future, the choice is straightforward. If you're looking for range and variety (particularly if you're inclined to delve into the area of audience or other non-commercial recordings) and working on the likelihood that you're not sure what directions your ears are going to be following over the next couple of years you'd more or less have to go for America.
There's also the matter of future technologies to deliver content into the home (I'm thinking of Moogis as an example) which are more likely to emanate out of Silicon Valley than Surbiton.
Looking to the past it's a different matter.
For a start there's the question of whether you're revisiting past glories or seeking out stuff that you missed the first time around.
Ben's white folks limitation makes it easier in a way. Under that ruling you could still hear the old blues and access the extensive catalogues of the R&B labels, so on one front you could go British, get the white folks take on the classic blues and still have the originals to refer back to.
Another issue raises its head here. The conventional wisdom is that the likes of the Rolling Stones took Muddy Waters and Chuck Berry, placed their own twist on the music and re-exported it in a classic coals to Newcastle scenario.