The answer is going to depend on what type of sample it is that you are trying to dry out, and possibly also why, and what constraints you might have (e.g. keeping temperatures low enough, avoiding "cooking" the sample, etc etc).
I agree with Paul. Results depended on the type of sample material and structure. If samples are biological you cannot use a microwave oven at all. Please keep in mind that a microwave oven will heat water inside the sample. If water distribution across the sample's volume is not evenly heat also will be uneven. I think that with hot air you'll get the same. Rotating the ample around all 3D axes may help.