Emperor Palpatine, Sith Lord #59 Revenge of the Sith Star Wars Miniatures Very Rare

This is probably the best version of Palpatine/Sidious out there, especially for the Imperial faction. He draws in practically a third of the Grand Republic Army with his commander effect, is immune to fire from same said forces, can dish out some nasty damage, and his betrayal ability is a real tide turner, having myself been able to use it to turn Jedi Master Luke Skywalker, General Mace Windu, and even Boba Fett, Bounty Hunter during games.

And to give him even more punch, pair him up with either Governer Tarkin or Mara Jade Emperor's hand. If you do use the Governor Tarkin trick, just make sure to sling along Mas Ameda, too.