I find that the US customs agents are much nicer then the Canadian ones
I find the Canadian ones nicer, but my expectation is that this is because I am Canadian. I expect that the border guards of any country show a more positive attitude towards their own citizens.
That said I have encountered rude border guards only once or twice in my life ANYWHERE, and I'd put that down to those individuals rather than a trend.
I have got more or less of a runaround on different trips but never been treated badly. The few who were rude obviously I just sucked it up and kept my "your an asshole" thoughts to myself. Arguing with a guy who has the power to pepper spray you, tazer you, throw you in a jail cell, and subject you to a full body cavity search, not to mention make notes on your file that will cause you grief for years to come--not smart.
I have to say though--
I like the Chinese system. They provide a little electronic survey for all passengers to fill out, post customs, where you rate how professional you thought the customs official was, and it is linked to the guy who interviewed you. I imagine they occaisonal negative comments but if one guy keeps consistently getting negative reviews he is spoken to.