I guess it depends on what you look for. I haven't bought a flight in a while, but I just looked at kayak and google flights for comparison. Google flights is a much simpler, more direct UI, and it feels a lot more responsive. In particular, kayak violated one of my huge personal pet peeves: page content moving around while it's loading.

That said, the gap is a lot smaller than it used to be. There was a time in the past where google flights was light years ahead of priceline, kayak, etc. in bloat, bugginess, responsiveness, etc. That gap has shrank considerably and it's more a matter of preference today.