L-M I've owned various iterations of Yamaha, Kawai, and Casio, digital pianos and keyboards.
Yamaha is very reliable. If you like what you feel and hear, it's a slam dunk. They make some serious acoustics and own Bösendorfer. That's some serious creds. I sometimes feel that Yamaha can be conservative, although that doesn't mean they aren't at the forefront in practice.
Casio can be quirky, and I say that in the best way possible. I've had a lot of fun with quirky and I have a lot of fun memories with various Casio instruments. I actively use Casio instruments that I would never willingly part with. If I had a choice though, I think I'd pick another brand for my digital pianos. I haven't spent too much time on their hybrid pianos though, and those seem to get good reviews.
Kawai is hands down my favorite of the bunch. In my opinion, they are super innovative, and continue to push the forefront of technology where it matters. They also try to pack the best package possible at every price point. They aren't giants like Yamaha, but I would go Kawai digital over and over again. They certainly aren't asleep at the wheel, although the industry as a whole is in a tough spot.