bolt seems like the best balance between killing problem creatures and still being slightly useful against combo decks.
This is just a sort of general strategy I believe, and maybe not directly applicable to your deck, but I think people overvalue card flexibility in vintage (and legacy, back when I played it). Even though you might play against an Aggro deck and a Storm deck in the same tournament, you won't be playing against both an Aggro deck and a Storm deck in the same game (Mentor TPS notwithstanding). Cards that improve your card selection actually reward you for playing with more conditional spells.
It's hard to objectively rate how good a card is, but humor me
Consider running 2 cards that you would rate "a 5 out of 10" against Storm and Aggro. Compare that with running 1 card that's "a 10" against Storm (but dead against Aggro), and 1 card that's "a 10" against Aggro (but dead against Storm). On average, when you draw a card, the outcome is about the same with either option.
But once you start dealing with card selection, that's thrown completely out the window. Cantrips, Tutors, and Looter effects all make you more likely to find, the cards you need, and less likely to end up with the cards you don't. Consider playing a Preordain or activating a Dack Fayden and seeing 2 Lightning Bolts vs seeing 1 Mindbreak Trap and 1 Supreme Verdict (For the sake of argument, assume those cards are stronger than Bolt against their respective opponents). This is a case where running flexible cards makes your deck LESS flexible.
Whether that applies to your specific deck has a lot to do with how many card-selection effects you have, and how powerful your conditional cards are compared to your flexible ones ... Just food for thought!