Personally I'd say Civ 6 despite preferring the classic style and layout of Civ 5.
Both games are good, but Civ 6 is probably the most balanced in my experience.
In Civ 5 the end game suffers IMO. I dislike how they implemented the United Nations mandatory voting thing, especially when you're the leader and your Proposed options begin to run out and you have to start proposing things that you don't want because the game forces you too. It's so frustrating, even preventing you from leaving the UN altogether. Honestly that whole update annoyed me so much I would stop playing at endgame. Also in Civ 5 the AI tends to be random and all over the place. Example; someone declares war on me, I stop the invading force and take one of their cities they founded nearby (miles away from their capital.) Afterwards everyone hates me and thinks I'm a warmonger for the rest of the game.
Performance wise I play both on a 2500k and 7970 3GB 16GB with no problems at 1080p.