Originally Posted by
DNSolver
Putting Sphere in off of Show and Tell shuts off the Omniscience kill for at least a turn.
The problem with Chalice is that some decks that fold to it (namely Delver) are already very easy matchups. The consideration is the Miracles matchup, where you would be fine with having Chalice, except you probably also want discard spells, Pithing Needles for Top, and access to 1 mana searches such as Expedition Map / Crop Rotation. I have found discard spells to be good to stop Blood Moon / early mentors / Jace / wear/tear and more in conjunction with Surgical Extraction. I tried Chalice for a while but unless we are interested in cutting a ton of our 1-drops postboard (such as -8 discard -4 crop -1 X) for +4 Chalice +4 Surgical +1 Needle +4 Decay) but then you are boarding in Chalice and Surgical. I prefer Sphere because Surgical can still be cast in the matchups where we want both (BR Reanimator, Storm, Show and Tell).
I still have Chalices in paper but I'm trying to get rid of them for Spheres.