>>715772802 (OP)5 has less convoluted mechanics and is more straightforward. In 5 you won't need to worry about adjacency bonuses or district placement. You just build your cities in places with plenty of resources or strategic defensive locations and progress the game. In 6 you would need to know, almost from the start, that a random wonder only available in the modern era will need to be adjacent to a lake tile, a hill tile and a campus district or whatever bullshit.
On the other hand, starting with 6 is not a bad idea since you have the Eureka mechanic, which is a small research/culture bonus you get when you do some specific actions in the game. I really dislike this because it sort of forces you to follow the same behavior no matter what civilization or style you are playing, since you want to research and advance your culture as fast as possible. But, as a newbie, it is continuously telling you what to do next, so it can serve as a guide on how to properly progress.
6 also has some really bad barbarian behavior and climate change events that don't make much sense. For example, building next to a volcano is absolutely OP, you will get half of the map flooded by 1800 because of ice melting and stuff like that which, in my opinion, feels very forced. In 5 you will be able to decide your roads and have your workers around much longer, so you also get a better feeling of control over your civ and your territory.
Overall I recommend starting with 5. If you try 6 you might not like "going back" to an older game that has more or less the same mechanics but looks outdated and feels simpler. Oh, and I almost forgot about Civ 6 counselors. For some reason, they decided to add 6 or 7 old cunts that are the same for every civilization that you can hire to get specific bonuses for your civ. They are like part of your government I guess? I never liked them.