I got into Civilization rather late with their fifth entry. I was hesitant because as I get older I need more time to game than I do new titles. Still I picked up six with all DLC during the last sale. I have to say I am liking the changes. It was good to wait because Civ does need its DLCs to feel complete.
On a side note, it runs quite nice on the Steam Deck (In desktop mode docked)
IMO, Five is easier to learn and more straight-forward, while Six feels more convoluted, but Six gains some depth and variety from that if you put in the time to learn it.