Poking around a bit, I found quite a few graded cards posted on eBay, and while sellers were asking higher-than-average prices for those cards, one thing seemed pretty obvious: The newer a Magic card is, the less likely grading it will have a significant effect on its value
While this will mostly be relevant in casual play, it's worth pointing out that if you have a Naban, Dean of Iteration on the battlefield, every Wizard that enters the battlefield will trigger Warstorm Surge, Fathom Mage, Angelic Chorus, and Purphoros, God of the Forge (among others) an additional time, which opens up an entirely different layer of deck-building potential that was missing with Panharmonicon, which only triggered abilities on artifacts and creatures
Prices are updated based upon Magic Modern Horizons 3 listings that sold on eBay and other marketplaces
Valgavoth does not gain immediate card advantage but has a static effects that can accrue far more value than Atraxa in the long run
Gran-Gran Avatar: The Last Airbender will also feature both Commander Box League events and Two-Headed Giant Commander nights