So, after being owned in PvP countless times, due to some silly things such as people outrunning me, running out of Stamina/Magicka mid-fight, not having enough CC's or simply not doing enough damage, I've came up with a build that I've found very viable in PvP.
Race: Khajit - Although I went an Argonian, I do strongly recommend rolling a Khajit. Their passives are very viable for a Nightblade. 15% Health Regeneration increase in Combat, Stealth Radius 3m increase, increases Crit Chance by 3% and damage done by successful crits by 15%.
Atributes:
49
Magicka
0
Health
0
Stamina
This will allow you to have enough Magicka and Stamina capacity/regeneration to last you in fights and do a bit more damage, as well as enough health to live long enough to do some damage and boost your Leeching Strikes.
Armour: Medium - I strongly recommend this. With all the passives unlocked, 21% Crit Chance increase with weapon attacks, 28% Stamina Regeneration increase, 21% Detection Area decrease, 28% Sneak Cost decrease, 10% more attack speed, 28% Sprint Speed increase and 28% Dodge Roll stamina decrease.
Weapon 1: Dual Wield Daggers
Daggers will give you 5% Crit Chance increase, which is better than the other weapons (IMO).
I chose dual wield because it does the most damage by far, and it has a snare which we wouldn't have with the 2h.
1: Ambush - It was hard to decide whether to use Ambush or Lotus Fans, but the damage done from Teleport Strike from sneak was just too much to give up, and the extra 30%-40% damage boost on the next attack is nice too.
2: Surprise Attack - Does a decent amount of damage and will do more with the 30%-40% damage boost from Ambush, plus they'll have 40% less armour.
3: Rending Slashes - They're probably gonna be getting out of that stun now, so you're gonna want to put a snare on them, and the DoT isn't too bad either.
4: Rapid Strikes - Does a lot of damage and increases attack speed by a decent amount. You can use this ability twice, or once and then auto attack them until they're on low health.
5: Impale - This can be easily swapped for
Killer's Blade; but in my opinion, when people are desperately trying to run away when they're near death, Impale comes in handy.
Ultimate: Flawless Dawnbreaker - 13% weapon damage passively is pretty amazing if you ask me.
Weapon 2: Bow
It's important to have a ranged weapon, as in massive PvP battles you don't want
to keep dying or have to sit back all the time.
1: Swallow Soul - This does quite a bit of damage, it'll allow you to live for a bit longer and passively heals give you more health.
2: Bombard - This will root them for 3 seconds and snare them for 40% for 6.5 seconds.
3: Venom Arrow - This is a nice ability to use your stamina and also finish off targets.
4: Magnum Shot - A nice CC and it'll get you out of range from your targets when they get up to you. The damage isn't half bad either.
5: Shadowy Disguise - I recommend popping this fairly often. You should have quite a bit of Magicka to waste with your bow out, and this will give you a critical on your next attack (I recommend using Poison Injection after popping Shadowy Disguise). Not only will you crit, you will get a decent amount of Spell Resist (and armour if you're in PvE) for 4 seconds after it. It will also increase Stamina Regeneration by 30% for 6 seconds.
Ultimate: Flawless Dawnbreaker - I recommend Flawless Dawnbreaker again, 13% passive weapon damage seems to be unbeatable as oppose to an ultimate ability which isn't going to be used very often.