Which commander you pick to lead your army depends on you: what colours do you want to play, which strategy do you prefer, and how cruel to your opponent do you want to be
It's not because they break some amazing combo or recently printed card in order to justify the price spike
Common is black, uncommon is silver, rare is gold, and mythic rare is a bright orange
A High Market in the manabase, or creatures that have sacrifice abilities, or just an Oketras Monument to provide cost reduction all things that can enable Skullclamp
Stayin Alive Of course, a six-mana board wipe alone isnt going to get Dimir Mill through a game of MTG Standard
Karmic Guide is similar in its use: it can be a decent card to take advantage of some mild graveyard effects, or it can be made part of a combo