President of HTC USA Jason Mackenzie answered some question of the users on Twitter about the update for the Android 4.3 on HTC One. See the thread here.
As he says the Android 4.3 Development for HTC One is right on schedule and the update would start rolling out in the last week of this month as the company promised earlier. This news goes for both the US and the EU US HTC One devices.
Seems like the HTC would be starting to roll out updates and would win the race as it appears now, as Samsung is supposed to bring this release to their smartphone by October, and Sony has not yet even announced the update schedule for the Xperia Z Smartphones.