You'll have far more control of the downsampling procedure, and can tailor it to image content. The camera will downsample the image itself, but with no control over it by you. Unless you need to get the downsampled image as quickly as possible, PhotoShop is the way to go - you could also crop, employ multi-pass downsampling using both the bicubic and bicubic sharper algorithms (although in CC the algorithms should work better when used alone than in older versions), etc.
Or use other tools with different, newer algorithms, i.e. Catmull-Rom - all depends on what kind of quality you need at the new size and resolution.
As Neuroanatomist said, you'll need some final sharpening at the final size - downsampling does clear out sharpening haloes made before. What kind of sharpening to apply depends on your sharpening workflow.