Providing fun and interesting build-arounds that help to keep the clock moving is one thing, but marrying that up with Commanders that allow the true Control players playstyle to shine through is inspired
Caesar hits so many favorites for me: hes inexpensive, hes got a decent power and toughness, and with a little sacrifice, he becomes a problem quickly while doing everything that Soldiers wants to do, make more Soldiers and deal damage
Four mana for a 1/5 isnt amazing, but it does start placing counters immediately, and potentially drawing cards too
Kaalia is has been among MTGs best commander decks for a long time because cheating mana costs is almost always broken, so with Kaalia you want the biggest, baddest creatures of the types you can find, like Avacyn, Angel of Hope or Vilis, Broker of Blood
You can give your opponents planeswalkers more loyalty, increase the number of +1/+1 counters on their creatures, or even just give them additional resource counters like oil counters