Super happy with my Brooks C15 on my gravel / commuter bike. Comfortable even without bike shorts, and with bike shorts I have ridden it up to 300km in a day with no discomfort whatsoever. It's got well over 15000km on it and it still looks good as new - if it broke tomorrow I'd buy another just like it to replace it. It's considerably more comfortable to me than the B17 I have on my folding bike, and weatherproof to boot.
The Giant Fleet SL on my road bike, however, isn't quite as good, but it's not bad enough to warrant replacement at the moment.