Basically, this would be ideal for me;

Killing Random Hostiles (aka Evil NPCs/Creatures) - No Karma Gain
Killing Very Evil Karma Neutral Faction NPCs - Slight Good Karma
Killing Good Minor faction NPCs (Goodsprings, Novac, Followers) - Slight Bad Karma
Killing Neutral Strip Factions (MP, Securitrons, Chairmen) - Slight Bad Karma
Killing Evil Strip Factions (Van Graffs, Gamorrah )- No Karma Change
Killing Very Evil Members of Strip Factions (Mortimer, Head of Gormorrah Faction) - Slight Good Karma
Killing Opposing Faction Members (aka if you have a high rep with the NCR, kiilling Legion) - Good Karma
Killing BoS Faction Members - No Karma
Completed Good Result Sidequests - Good Karma
Completed Bad Result Sidequests - Evil Karma
Completed Neutral Result Sidequests - No Karma
Completing a Faction Quest Against an Opposing Faction (e.g. if your rep is high with Legion and you complete a quest against the NCR) - No Karma

And you should gain and lose karma no matter if you sneak attack someone or not. It should remain consistant.