I'm not exactly in a hotbed of earthquake activity (we've had two in the 17 years I've lived here), but it will be on carpet floors. A brace might not be a bad idea. Nothing a little spackle can't clear up when we decide to move. I think it will ultimately depend on which I buy (so whichever is cheaper :P) and how shakey it is.
Olympia, I was thinking about the python, too. I use it on my QT tank that sits on the ground. That will probably be my best bet. It really doesn't create strong suction, but it's the best I have.
Since I'm going to change the substrate on one of the tanks I plan to move around I'm going to wait until I have the sand to do this. It's going to be one long day of moving tanks and changing substrate.... blegh!