The most efficient way to climb, is by maintaining as many contact points with the bike as possible. Seated climbing is therefore the most efficient way to do it. ‘Most efficient’ doesn’t usually equate to fastest, or most comfortable though. So to get the best balance, remain seated where the gradient is steady, and get out of the saddle in upwards corners / hairpins, and on any bits that ‘step’. If you’re after speed, at any cost, stand up, push your hips forwards, and downwards, and keep your shoulders down, and your head level. It’s not efficient, or particularly comfortable, but it is a way to maximise speed. Watch how Vincenzo Nibali does it, that’s about perfect.