I have spent hundreds of hours playing Civilization 2, 3, 4, 5, and 6. I'm young for Civilization 1, I guess. Civilization 6 is somewhat of a disappointment. I think the game probably peaked at 5, though I still play Civ 4. I think Civ 4 has the best historical scenarios.
Civ 5 is amazing. I kinda like 6 but it totally destroys my favorite playstyle (very small empires). In fact I'm civ 5 my absolute favorite nation is Venice lol. I just rush crap tons of world wonders concentrated in one city and make Venice ridiculously powerful.
Civ 6, the AI Empires will vigorously put a city on every empty scrap of land as quickly as possible. Worst of all, the AI is very bad at picking strategic spots, so when you conquer their cities I constantly see "the city would have been so much better if you moved it two squares to the right!" Civ 3 was the last Civilization game that gave you an option to remove unwanted cities. It hasn't been back since.