On The Fence

One who is facing a choice but is "on the fence" has not decided what choice they will make. Example: "Which school do you prefer?" Answer: "I don't know; I'm on the fence."

You are on the fence when you have not yet decided. Example: "Has he decided whether he will take the job yet?" Answer: "No, he's still on the fence."

You are on the fence until you commit yourself and make a decision.