There's a reason this is "Favorite Final Boss" instead of "What gaming publications think is the greatest boss of all time." Also, isn't Gamespot the same publication that fired Jeff Gerstmann for not giving Kane and Lynch a stellar review? That should show you how intelligent they are.
My FFX fanboyism is going to come out here, and I'm going to say Sin/Yu Yevon. I love the way the Sin fights are set up, with the slow weakening of Sin until you could get inside of him. The BFA fight is well done, save for the fact that he doesn't have a whole lot of health. Like Dodie said, I like the extra little bit of strategy that Tidus' "Talk" command gives, and I really think it solidifies that Jecht still has some humanity in him despite being what he is.