Whatever gets you to the top.
Actually, I must have missed the memo that said you have to maintain the same cadence on hills that you maintain on the flats. On gentle grades, perhaps, but the steeper the grade, the more this becomes difficult, at least for me. I've heard a different rule of thumb that you should aim to pedal 75%of your usual cadence on climbs.
Rules of thumb aside, use the gear that allows you to balance the strain climbing puts on your legs and lungs. That's going to mean a different gear for different people, depending on their respective leg strength and aerobic capacity. I have one friend who can spin fast up just about anything, alla Lance Armstrong, without blowing up. Most of us, however, cannot aerobically handle that and have to spin a bigger gear (or little gear in my cas) at a slower cadence.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher