I assume that you are looking at the 2007 Buell? For my money, the 2010 they have would be a better deal. 2008 and up Buells were improved over earlier models and the 2010 was the best of all.
I have a friend with both an 1150 GSA and a Buell XT. He says the Buell is sportier but the BMW is more solid and reliable. He likes both but says if he had to keep one, it would be the BMW.
If you want to save some money, do a fly and ride. Both bikes are cheaper in the US and both are eligible for import.
2005 GS1150 Adventure - Range Rover, 2002 DR650 SE - Land Rover
"Not all who wander are lost" - JRR Tolkien