There are more commanders that work in this space these days, but the Bant colors serve the walls archetype well
Tormod is definitely the stronger of the two because black works better with the archetype and zombies have considerably more support that spirits, but you'll realistically play either one in your gravebreak deck, assuming your colors support them
Of the sets source material cards revealed up to now, each of them have been screenshotted from the series original release as was broadcast on Nickelodeon and eventually released on DVD, with the only changes made, if any, being to their brightness, contrast, and color saturation (and sloppily too, as seen in the Agent of Treachery below, where Azulas blue flame has the very distinct up the saturation, up the brightness halo effect)
Do you need the newest cards for a tournament in the next few weeks
Master Transmuter - Cheat and re-cheat the best creatures Cloud's Limit Break A modal masterpiece