I chose the Nikon Z 180-600mm for its incredible value and reach, but my chiropractor would likely recommend the lighter Z 100-400mm. While the 180-600mm is my favorite lens, offering a dream 600mm focal length for wildlife and sports, its size and weight (2,140g) are significant.
The Nikon Z 100-400mm, though more expensive, weighs only 1,435g and is much shorter. This makes it far easier to hand-hold all day and pack in a kit bag. For photographers with back concerns or who don't absolutely need 600mm, the 100-400mm's lighter build and faster aperture range present a compelling alternative.
Both lenses deliver superb image quality. The 180-600mm remains the most affordable path to 600mm on the Z system. However, as used prices for the 100-400mm have dropped, it has become a more accessible option for those prioritizing portability and comfort without sacrificing optical performance.