Dueling is one of my favorite things to do and I think DKs are particularly strong in a 1v1. I do run into builds and players who outplay me but the below build is extremely hard to beat and has brought a lot of success:
5L/1H/1M - Shacklebreaker + BSW + Bloodspawn (if you want even more damage Grothdarr/Skoria but I think it's enough)
Front Bar S&B: Flames of Oblivion, Whip, Burning Embers, Fossilize, Talons (or chain) ULT: Dragon Leap
Back Bar Resto: healing ward, harness magicka, wings, volatile armor, entropy ULT: Resto Ult or Bats
Max Magicka Sits at 39-41k, 20k health, 17k stamina. Spell DMG: 3200 when BSW procs Weapon Damage:1400.
Also, the above comment about Sloads isn't wrong but honestly you'll get so much *** and rightfully so because it's your set playing and not you.
This build is especially good against the shield stacking sorcs who beat everyone else.