If you want the sharpest possible edge and don't mind caring for a harder, more brittle blade, buy Japanese; if you want a tougher, more forgiving knife that can take abuse and be honed casually, buy German. Japanese knives, like the gyuto, are ground to a much sharper edge angle, typically 15 to 18 degrees compared to 20 to 22 degrees on a western chef's knife, and use harder steel that can exceed 60 HRC, which is why they cut with such precision but also chip more easily. German knives are softer and more ductile, so they resist chipping and bend rather than break, but they won't hold that razor-sharp edge as long.
A Japanese knife is not the right choice if you regularly cut through bones, frozen food, or hard squash, or if you're used to rocking the blade hard on a cutting board, that lateral stress and impact can chip the edge. German knives are the better everyday beater for heavy prep, but you'll trade away the effortless slicing and fine edge retention that make Japanese steel so satisfying.
The gyuto, literally "beef knife," is the Japanese take on a French chef's knife, with a flatter profile that suits push-cutting and slicing. That acute blade geometry is only possible because of the harder steel used, a typical western knife at 20 to 22 degrees would roll or dull quickly at 15 to 18 degrees, whereas the harder Japanese steel holds that finer edge. That's the core trade-off: hardness buys sharpness and edge retention, but it also makes the blade more brittle, so you need a gentler technique and a wooden or plastic board. For more on how these knives are built and what to look for, see the Knives and Stones Education Centre.