Sinister shield. Imo it's the best designed and most indepth feat. I love this feat because it's not simple. It makes you think and it punishes you if you waste it. It's the most interesting feat in the game. It has so many tactical uses. It forces you to step back and look at the overall picture and help at a distance or waste it completely and injure yourself.
No it's not the best feat but imo it's the best designed feat....except the glitch were you give a shield to a dead revive symbol.

In any case I love this feat because of what it brings to the game.