Theres a real argument for Simic and Mardu, but Mardu is sorely lacking in a +1/+1 counter commander
Of the top decks in the format, Heartless Act will always have some target to take down
While this can be a threat, and you should watch out for growing Ornithopters, most of the time that means that you will take no combat damage and more than half of all decks rely on combat damage to win the game
They cost more mana for a reason, offering larger stats, more powerful effects, or game-warping value engines
Therefore, the use of proxies is sometimes further constrained to only one method of fabrication, for instance
5 Edgar Markov Just One Bite Vampires have never had a better commander than with Edgar Markov