My favorite is CivIII, but I've been playing since the very first one came out. I actually bought Civ 1 and had to wait three months to play it because I had to upgrade my EGA card to a VGA card.... Old school!
Anyway, I've played all of them, but I probably play Civ III the most. I have not yet purchased Civ 6 as I mostly enjoy PVE, and I've read horrible, horrible things about the AI in that one.
As for D&D, I've been playing that even longer than Civilization, and each game is going to be different based upon the DM for sure.
Thanks for the warm welcome!