advice i've received is that's it's good to have two depth areas in mind that you might take, try and be prepared for both. then during the exam, if you're in a state where you're able to, look over each section quickly and see which one you think has easier problems (or at least ones you can do) and go for that one.
I have to disagree with this. Pick a depth in advance and stick to it. With only 6 minutes allocated per question, you probably won't have any time to spare in the afternoon to look over an additional section. The time you waste looking over another section and debating which one you should work on could be better spent answering questions in whichever section you prepare for in advance.
FYI, here in NC, you have to declare your depth area in advance on your application.