Great question.
This is quite easy to dissect, depending on what you mean by “fight”.
In a fight to the death? Toppo takes the win 9/10 times.
A fight where killing is not allowed, Broly takes it 10/10 times.
Why do I come to this conclusion?
2 factors:
- Destruction energy
- Control
Now let’s establish some things. There is a HUGE gap in power between Toppo and Broly.
Broly is massively beyond super saiyan blue level, this is proven multiple times:
- Broly tanks a punch from post-ToP God vegeta just in his Ikari form
- Trashes God Goku
- Absolutely nullifies a full powered galick kamehameha from goku and vegeta in blue
- Pushed goku and vegeta to fuse, then pushed Gogeta to use at least super saiyan
So it’s clear that Broly is way stronger than Toppo, who scales to blue evolution vegeta and super saiyan blue kaioken goku:
The outstanding factor here is that in a fight to death, Toppo would be able to use his destruction energy to it’s fullest.
We clearly see in the anime that there is a clear difference between using destruction energy in the form of ki blasts, and using the actual destruction technique.
Toppo quite literally expresses that he was holding back his use of destruction in fear of being disqualified:
So he instead resorted to spamming destruction energy ki blasts, that he could alter the strength of in order to prevent his target from dying:
It’d be completely inaccurate to say things like “Destruction energy won’t work on those stronger than you”, when quite the opposite has been implied:
In addition to this, we actually see the hakai technique used successfully on more than one occasion:
Plus, Toppo can nullify ki attacks completely:
And surround himself with energy of destruction:
“WeLl TreY,, VeGeTa PUnChed tHroUgH ToPpo’s eNerGy oF dEstRucTioN and BrOlY is WaY sTroNger”
Vegeta did this by focusing the essence of his blue evolution’s god ki into his fists, which countered the destruction energy:
The same way Goku did the opposite by focusing all of his power in super saiyan blue into his fists to use the destruction attack
Broly is not equipped with god ki.
Now while Broly may be stronger, he lacks the adequate control to put Toppo down before he finishes him off.
If killing were not allowed in this battle, Broly takes the cake 100%.
In a fight to the death, Toppo slaughters 95% of the time, and the other 5% is due to him underestimating Broly.