I always find myself wondering how people forget Ganondorf's U-Smash has IASA frames after the impact of the kick, making it the actual fastest U-Smash in the game. The attack can set up mind games in neutral, letting your opponent's guard come down most of the times; this can allow for you to use F-Tilt, D-Tilt, F-Smash and D-Smash (most recommended of the few) when they do.
Due to its speed (which is about as fast as Jabs in this game), it's also one of the few (if not the only) U-Smashes that can combo into itself, linking up to an absurd amount of damage, almost at 50%. If you connect two U-Smashes, then a combo will be very easy to perform with U-Air.
This attack can also lead up into dangerous combos and is also very dangerous to get above; one, it can lead into a U-Smash > U-Air combo easily, and two, its sweetspot is on the top, allowing him to KO at very early percents. So if you're caught in the air by it, chances are you won't be going good any time soon.
It's his safest option in Neutral, thanks to the mind game he can bestow upon the opponent, the high damage it gives off, combo ability and overall the speed. It's a safe attack when blocked by the opponent, no less.
I'm not making it up or exaggerating this; this all came from testing and obvious knowledge. There isn't any U-Smash that's faster and as lagless as Ganondorf's. It has a tiny amount of start up lag, but no end lag thanks to the IASA frames upon the peak of the attack.