I personally hold Brown in a high regard, as well as Princeton (as long as you are not a Caribbeanist). I would avoid Yale at all cost, even if that was the only one that accepted me. As for Harvard, I am not too crazy about the program but you have to admit that the name carries a lot of weight and prestige. In this dynamic between Oxford vs X-Ivy, I would definitely choose Brown (always), seriously consider Princeton, Harvard and Oxford for me are pretty equal. Yale is a NO for me. Seriously, that department has a lot of problem and simply switching some professors around but keeping them is very problematic for me. That just shows that they care about name recognition not the safety of their graduate students.
Although not mentioned, I do like Cornell a lot and Columbia, though talking to some of the grad students made me nervous about it.