GT. Wagons are boring as shit. I can imagine in the US the novelty factor might be quite high because you don't get so many of the tourers over there - over here they're abundant, and simply blend in. The GT looks different (and pretty good in the flesh, IMO).
Also, as I've always felt, the tourer doesn't offer as much benefit over the saloon as the GT does. I think if you're going to compromise the cars dynamics, you may as well get a useful amount more space (passenger & luggage).
IIRC one of the reasons why there haven't been more M wagons in the past was to do with the rear suspension layout compromising/being compromised by the load area.