For the way you asked this question, i'd have to answer Spain.
I play confidently at immortal, the more so if it's a civ that can follow a certain strategy easily. But Spain is the odd one out of all civs, it's bonus completly depending on luck or circumstances. And yet, this makes them very appealing to me whenever i wanna have a game just for fun. it's always a surprize what you are going to get, usually i manage to atleast settle one natural wonder with Spain, but often the specific wonder and time you get it can get it can have such an inpact on the game that it kinda asks for very circumstancial strategy's. With other words, Spain can be played in a lot of different ways depending on what happens, finding the production boost of Salomon's first might set you up for early conquest or say early wonder spaming. Fountain of youth will motivate you to quickly set up a large empire withough needing much workers in the expansion phase to keep control of the happyness, or say allow you to plant city's on very productive spots withought needing to care about the luxury's. Finding Mount Sinai can send you on diplo win route where you try to dominate with faith early.
Spain is just fun, it's strategy's usually highly circumstancial beyond the point of simply building sufficient scouts at start. The effects of double gains on natural wonders + double gain on faith from natural wonders is often somewhat OP but it takes addapted strategy's to make the most out of it, the more so because you lack advantage's beyond that.
