Rengar:
Pros: Can leap from bushes, tanky from W, can go invisible with ult
Cons: He got nerfed so hard.
Nocturne:
Pros: High ass damage, Spell shield, Ult is a great ganking tool, fear included, passive gives him healing every couple of shots
Cons: Hit him and he will probably die. In other words, if you dont kill him before the fear, you die.