Evil.
I habitually kill charmingly pleasant NPCs just to see if they have nice stuff I might want. I get that little thrilling shiver right to the core when a game not only lets me be evil, but plays along with it well.
In every infinity engine game it usually resulted in everyone 'magically' going hostile on sight though so in those I'm pretty much limited to playing a half hearted neutral evil fellow (sensibly selfish).
Intimidation and theft alone don't really cut it for me. This is why I felt both of the Kotors evil paths weak. I felt like a pimp or street thug rather than a Sith Lord.
Most games that feature an evil ending are still too similar in the path getting there. The Geneforge games (especially #4) at least offer varied quests based on which faction you support, letting you work for the 'evil' Shapers or the naive Rebels or play them off againt one another.
As for the best 'evil' ending, I still enjoy Jade Empire's. The good ending makes no sense in that game.
Spoiler:only a bleeding heart idiot would free that moist bint after she promises you 10 years of drought as a reward... and what's she done for you lately but interrupt your sleep with visions of her floating about offering cryptic messages. Far better to keep ahold of her as a resource and screw the other kingdoms with drought. Did They capture a god? No they did not so let 'em cower.
