Short version : I think Stellar Has a better floor but Zander has a better ceiling : So Stellar = Safe , Zander = Risky
Stellar
Right now I think 100T should stick with Stellar, he's over-hated, more flexible than Zander, 100T also has a better controller (Bang), and stellar is a much safer option.
Zander
However, Zander has the most potential of any igl in NA and probably the world. But he's been struggling recently and struggles to adapt. I believe Sgarres would bring out that potential and make him the best IGL in NA and probably globally. However isn't practical right now, it would take time for Sgarres and Zander to show results, and it will also cost a lot of money. Zander has a crazy expensive contract with V1 and the way he's been playing recently the buy-out cost is not worth it, and even if you're confident he'll become the best igl. It will take time for Zander to show results, and in that time in between, there will be a lot of losses as 100T tries to find their footing. With franchising just starting it wouldn't be worth the money, or the risk to sign Zander over Stellar, especially when you have Bang who could overtake marved as best controller NA sometime in the near future.