What do you set it on vs 2 Card Monte (Grindstone version)?
I almost always play it on 1 in that matchup. You aren't going to lock them out of mana and by the time you ramp up to x=3 or 4 you would probably be dead anyway. Instead, this locks out Grindstone and most of their removal, so that's about as good as it's going to get. If they've already landed grindstone, I'd probably try to hit @3 to prevent Painter or Tinker from ending the game and hope that I have a Revoker effect for Helm of Obedience if they have a Leyline of the Void out already.
In general when you're blind on the play you almost always want to play chalice on 0 as this is solid against the field and allows you to play two lock pieces on your first turn. If you are in early game, then you probably play it at 1 if you're against a deck that abuses those spells (or in an aggro mirror where they're running Swords to Plowshares type spells) or for zero if you're worried about artifact mana making a difference. Late game, you simply need to think about what beats you: chalice@2 is very common to prevent Hurkyl's Recall and Ancient Grudge but I've also played it at 3 to stop Tinker, etc.
The main exceptions here are when you're worried about your own spells, e.g. Chalice@2 to block out Oath of Druids seems really great until you topdeck 2+ spheres, locking out Dredge's Nature's Claims isn't so good when you're depending on Grafdigger's Cages, etc. Not to say these can't be good decisions, they just require a bit more consideration.
EDIT: I guess I missed part of the question. I think the consideration of when to block out 1 versus a CMC of a hoser card depends on your gamestate. If you're running the game, you need to slam shut any windows they have left. If you're trying to establish yourself, cutting off their filtering and cheap removal might be the better call.