Without Power Armor: Large Deathclaw Gauntlet (3 claws). Massive amounts of melee damage. I wish I could wield two of them - on on each hand - to do non-stop slashing.
With Power Armor: Power Fist. Couple that with shock damage from the power armor arms and it is a lethal combination.
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i7 4790k @ 4Ghz, 4.4 Turbo
Asus Z97-AR
Custom Liquid Cooling
Patriot 16 GB (4 x 8 GB) 2133 @ 11-11-11-27
eVGA GTX Titan X @ Stock
Samsung EVO 1 TB SSD - O/S
Samsung EVO 1 TB SSD - Storage
Seasonic X-1250 Power Supply
Thermaltake Core X9 Chassis
Samsung UD590 3840 x 2160
Windows 7 Ultimate x64