To answer the question... for a scrapper, my nominations.
Katana/will. - With parry, you will never die.
For a brute...
SS/Fire - Easily one of the fastest killers in the game, very close to plant/fire permadoms. What you lack in defensive strength, you make up for in insane, raw attack power. A double raged burn will kill equal level minions with the initial hit, and the burn will kill lieutenants. Fiery embraced knockout blow will take bosses to half health. Build primarily for recharge, if defense is needed, pop a luck inspiration.
Titan/Elec: The two sets have fantastic synergy. Once you unlock the drain ability, you can sap entire mobs to bottomed out endurance with one press of a button, plus, your damage aura will keep their endurance bottomed out. this makes the 'ramp up' time for Titan weapon's powers a non-issue, and the killing power this set has, especially with a force feedback proc on whirling blow, is very high tier, plus, you have infinite endurance. Bonus: You're immune to sappers.
Claws/Dark: Brutes scale better with this combination, it's easy to slot recharge for, and focus on defensives with, plus, the Cardiac alpha will make the notorious Dark Regen energy cost nothing to you. You'll have a full health-bar once every fifteen seconds.
Stalker
Ice Armor and Energy Aura: Both have multiple layers of defense, and can achieve the softcaps with relative ease. Ice seems like it would be more powerful once fully slotted, but Energy Aura will level easier.