who has the best left hook in boxing today?

Donaire. If he loads it up well enough and lands it at the right target (jaw, chin, temple, ear area ) at the proper time, I think even the likes of Walters,Gardovich, Lomachenko and Gonzales right now at featherweights have no way but down and out. I have not seen a more frightening show of power via that left hook in the recent years than Donaire's shellacking of Montiel, himself a power puncher who is also deadly with the hook. Vetyeka was lucky to have not been hit squarely and yet he still went down. Reminds me very much of prime best Julian Jackson at middleweights.

Donaire has a great one but he loads up on it way too much, looking for one shot KOs. Mayweather has an excellent check hook but there's no significant power on it. Garcia got a killer left hook but it's SO obvious when he's about to throw it.

I would go with GGG or Chavez. Both to the body and to the head, their left hooks are deadly.

The hardest left hook for their weight division has to go to Gennady Golovkin by a small margin over Danny Garcia.

Mayweather may not have the HARDEST left hook for his weight but he has the best COUNTER left hook .

Rather the boxer have a good left hook due to power ,timing or a combination of both ,it's all about how they can apply it to their opponent.

Donaire by a mile i think Garcia power is overrated after He KO'd a fat old Morales, widely considered glass-chinned Amir Khan and a Lightweight Bum in Rod Salka. Now all of a sudden he's like Mike Tyson.

Mayweather and golovkin (he koed last time gaele by left hook and 2 more jabs if i am not mistaken).

As to HW: take a look at pulev. Not sure about Wlad though...never been impressed by his techniqus....other than the impressive accuracy of the punches....and the clinches...