That can also be used against you since you're admitting that you were not paying attention to your speed. It also means you lose the ability to claim that any speed the officer says you were traveling at is wrong, since you, by your own admission, wouldn't know any better.
"You tell me" is flippant and reduces your chances of leniency.
"Yes" could be used as evidence that your speeding was wilful, which probably isn't that bad but know that you're still giving them something.
I think "I believe so" or "pretty sure" was my go-to, but it's been a long time since I've been pulled over.
I actually don't even know that most cops actually ask this question. I think "do you know why I pulled you over?" is more common. To which you can often say "no" since you have no idea what actually went on in their head, but you might want something like "I can guess?" if you want to own up to some egregious action and show you were at least aware that it was wrong rather than acting as if you just drive like that all the time. But I can't tell if this is my real life experience or too many imagined interactions from message board discussions.
BTW "not that I'm aware of" when asked about weapons in the car etc. It shows that I'm aware of the technicalities and lawyerly answers (I don't know what they consider a weapon), but also engaging with them and their concerns.
That can also be used against you since you're admitting that you were not paying attention to your speed. It also means you lose the ability to claim that any speed the officer says you were traveling at is wrong, since you, by your own admission, wouldn't know any better.
"You tell me" might be a better answer.