Up and down - you can actually work more effectively by having flexibility to your posture.
Height adjustable desks are a trend that emerges every few years - and with good cause. Being able to sit, or stand whilst working allows a user to remain alert and refreshed. Some tasks - like making telephone calls, are easier when standing. Originating in Scandinavia, the idea has really moved along as more people are converted. And thankfully, as a result the prices are about 75% less than they were 10 years ago. Which makes a welcome change.