We all have that deck that just survives even though it isn't the best. For me that's [[Torgaar, Famine Incarnate]]. It's not the best mono black commander in any way but its particular combination of effects to me is emblematic of mono black. It's a bit of a swiss army knife and so I find myself hard pressed to really change anything about the core of the deck.
[[Trostani, Selesnya's Voice]] and [[Queen Marchesa]] Long may she reign! These were two of the first decks I built by myself and countless decks have been built and taken apart since them and they're still here and still get played.
I hate when people durdle...I recently built a [[Kami of the Crescent Moon]] deck to force people to draw all their cards so we all have options and answers. I love sitting across from 3 people and we all have a grip of 20 cards, let's make this game pop off!