The Jedi Purge and the rise of the Empire are two different but intertwined events. The Grand Plan consisted of wiping out the Jedi and taking over the Galaxy. Because this is purely about the Jedi Purge, I would say that Bane or Vitiate should not be on anyone's list since they had nothing to do with it.
Sith
1. Sidious
This was ultimately his plan. Plagueis did convince Sifo-Dyas to create a clone army, but Sidious was the one who convinced Plageuis that the army should be used by the Republic and the Jedi rather than against them. He was the one who started the Jedi purge by commanding Vader to storm the Jedi temple and commanding the clones to execute Order 66.
2. Vader
Shortly after Anakin killed Mace Windu, Vader stormed the Jedi Temple with the 501 legion and slaughtered countless Jedi. He then spent many years hunting down and killing Jedi.
3. Dooku
Without the Clone Wars, Order 66 may not have been possible. The CIS were like the Communists to the US during the Cold War or how the terrorists are to the US today. Palpatine needed a bad guy that everyone could point at so that he could justify destroying liberty and democracy in the name of security. The CIS was an artificial terror used to spread fear, doubt, and uncertainty. The creation of a galactic army and the use of the clones would not have been possible without the threat that the CIS imposed upon the Republic and the Jedi. TPM showed that the Trade Federation alone was not competent enough to lead an army against the Republic. The CIS needed Dooku.
Jedi
1. Yoda
Against his own judgment, Yoda allowed Kenobi to train Anakin.
Yoda failed to kill Dooku twice. The first failure allowed the Clone Wars to take place. Yoda and the Jedi council found out that Dooku was the one who chose Jango Fett to be the clone template, but (to the best of our knowledge) did not try to act on this information.
The RotS novel states that the Jedi Order grew stagnant while the Sith kept up with the times and changed their ways. Yoda, being 1000 years old and the grandmaster of the Order, could be held responsible for this.
While perhaps not entirely his fault, many of the villains during the Clone Wars are all former Jedi. Barriss Offee, Aurra Sing, Asajj Ventress, Darth Vader, Count Dooku were all once Jedi. Barriss and Dooku in particular both grew disillusioned with the Republic.
If the Jedi had taken a stronger stand against the corruption in the Republic, perhaps Barriss and Dooku would not have betrayed/left the Jedi Order. Perhaps Ahsoka would not have left either.
Asajj, Aurra, and Anakin were all unfortunate cases of not having enough proper guidance. If Anakin felt more comfortable about talking about his relationship with Padme, perhaps the Jedi could have made an exception for him. The scene in RotS where Anakin tries to hint to Yoda that something is going on and Yoda being completely oblivious comes to mind.
Anyways, Jedi Order was doing something wrong and Yoda has quite a bit to take responsibility for.
2. Anakin (sorry, but screw the first post)
Anakin was still a Jedi when he killed Mace Windu. Anakin killing Windu gave Palpatine the whole assassination and "the Jedi are taking over" excuse. This allowed Palpatine to execute Order 66. Anakin also enabled Vader to storm the Jedi Temple and hunt Jedi for decades.
3. Sifo-Dyas
Was convinced by Darth Plagueis to commission the creation of the Clone Army in secret.