Ancestral Hall (4)
Lighthouse (5)
Monument (46)
Ancestral Hall (7-3=4): And here comes the previously announced downvote for the Ancestral Hall. While being a great building, I think the opportunity cost of the Govt.Plaza is something to consider. Depends on your strategy, of course, and may pay off more often than not, but it is still a district locked to get the boni. Also, it kinds of forces you to a specific strategy, instead of being a more generalist buiding.
Lighthouse (4+1=5): At cost of not upvoting the monument, which deserves a +1, but has already too many (and is not just +2 culture, it's loyalty, and the border growth associate to that culture, which translated to gold, is quite a bit), I'm going for the lighthouse which, I think, I haven't upvoted yet either, and this way gets ahead of the AH. Of course, you only build it on coastal cities, but you indeed want it: trade route, food, gold, and normally housing... - чего еще желать? (read it in Peter's voice... What else can you wish for?)