That depends. Against a minion? Against LTs and Bosses? Not considering crits?
Let's do it the easy way:
Can't use claws because they aren't actually the same set.
Let's do dark melee.
Smite: 1.32 damage
Scrap mod: 62.562
Brute mod: 41.708
Scrap Smite: 82.582 damage
Brute Smite: 55.055 damage
Give both 95% enhanced damage
Scrap: 161.035
Brute: 107.357
For the brute to catch up to the scrapper, he needs 127% damage from fury so 63.5% fury.
But let's add 10% to the scrapper for crits over time. Say.. 159% buff or around 80% fury.
As you can see, for every buff to the scrapper, the brute has to work that much more to say even since scrappers have the higher damage modifier.
Be well, people of CoH.
And that's why my Elec/SD went from Brute to Tanker to Scrapper. Most bang for my buck. 
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Biggest Troll on the forums? I'll give you a hint:
Unless you are using said toon for farming and are consistantly above 80% fury. Then it goes to the brute. Also consistant damage when farming ends up being faster than inconsistant crits that may or may not hit when a mob would have been killed by the normal damage anyway. And patrons for brutes are perfect for farming with an additional 2-3 AoE attacks vs 1 for scraps and tanks.
How much Fury is needed to be on par with Scrapper damage?