Grohe Tenso in the boys' bath.
First there's the weight issue. You pick up the Grohe and it weighs a ton, it feels substantial. The Kohler feels lightweight, like it would buckle if you squeezed the faucet really hard. Then there's the finish. We went with the Kohler because we needed a brushed nickel finish to match the other fixtures (lights, hardware) in this bath. But the finish feels cheap, I think it'll chip if I breathe too heavily on it. The Grohe is smooth and I'm sure will resist every bang and knock for years to come.
Then there's the design issue. The Tenso is simplicity itself: push back, turn, push forward - each movement is straightforward , smooth and seamless. The Stillness faucet is rough, hard-edged and the pop-up drain is resting on the spout so it is impossible for anyone with limited mobility (or small children) to pull up the rod that controls the drain cover. I'm sure it will scratch the back of the spout too, but you won't be able to see that.
If we had purchased these faucets in chrome, they would have been the same price, but the quality? World's apart. That said, the Stillness is a pretty faucet and, as I knew I would, I made the plumber happy by choosing Kohler. After all that's what he has in his house.