I vote for the Four Seasons. The old Ritz's building is nicer, but the Four Seasons has better rooms, better service and better food (both their more casual Bristol Lounge, and their more formal Aujord 'Hui, both of which have recently gone through total renovations). The Four Seasons is in the midst of a total renovation (the old Ritz, of course, recently reopened after its own top-down renovation), but now that the lobby and the restaurants are completed, they'll do it in a way that will be near invisible to guests. That said, you might ask if any of the guest rooms have been renovated yet and try to get one of those. Even if you get an "old" room, however, they're still lovely, particularly if you get a view of the park.

I haven't stayed in the new Ritz, but its location, even though just around the corner from the other two, is not nearly as good.