It'd probably be younger me.
For better or worse I'm more interested in technology than history, so discovering the truth behind momentous events (ex: seeing the death of julius caesar, the sermon on the mount or whatever), having a casual conversation with someone important / interesting doesn't appeal that much to me.
I don't think there's anything about history I'd want to change, or that I thought could be changed. Though I think because it happened in my lifetime, I'd potentially want to stop 9/11 by choosing to meet with W Bush in 2001. it'd certainly be interesting to give W Bush a detailed history of everything that happened post 9/11, but I think besides preventing the Iraq war / 9/11 it wouldn't change much about the USA in 2018.
Though it'd be funny to stop 9/11 and the Iraq war, then go back to 2018 and find a nuclear war happened because Saddam actually did have WMDs.