“I don’t recall,” is always the best one.
How can anyone prove what you remember and what you don’t?
The funniest part of this line — used by people as similar as Ronald Reagan and Piers Morgan — is that there’s always the allowance for this further quote: “The minute I walk out of here, I just might remember. Life’s funny like that.”
A close second to “I don’t recall” is “I didn’t know.”
It’s classically political.
“I’ll let you do this, but if it anyone ever asks me, I’ll say I didn’t know.”