You want a slow weapon in your main hand in order to maximize the damage of your Sinister Strike. You want a fast weapon in your off hand in order to maximize the procs of Combat Potency.
For PvE, you will want to put Deadly Poison on your off hand because once it reaches 5 stacks it will start proccing the poison on your other hand, which will be Instant Poison.
Regarding weapon types, the best specialization for PvE is sword/axe. An extra hit > an extra crit, because it can crit by itself and can proc poisons. Fist/dagger can be used at lower gear levels because you will easily get your hands on a 232ilvl fist and dagger from FoS/PoS Hc trash mobs. Mace spec is not recommended as there simply aren't enough maces in PvE to keep the spec viable. I guess Blizzard just didn't like 1h maces when it made WotLK.
For PvP, you would go for Wound on MH + Crippling on OH, using either maces or swords, depending on your preference. You need Crippling because the passive slow from Blade Turning is unreliable. You put Crippling on your OH because it will be faster and because you will be able to use Shiv to proc it on demand. Check the sticky thread at the top of the class section for helpful guides.