I have to put another vote in for Canada. I'm a US Citizen as well, for the record, but have always travelled to Canada on my Aussie passport. Regardless of whether I'm going to Canada or just transiting through, I always get a grilling (compare this to US/UK/France/Germany/Australia, etc., where nobody even looks at me twice, just to confirm that I don't actually look suspicious

). I love it when I write "in transit to US" or "in transit to 3rd country from US" and I'm asked the purpose of my visit to Canada

. Or, I'm meeting a friend at Whistler to ski for a few days. "And why isn't your friend with you now?" "Uh, because he thought Sydney would be a bit out of the way on a trip from JFK to YVR."