I think in the past oxford and cambridge were the best becasue they had so much money and the smart half of the elite (the elite of the elite) went there. Nowadays given the old system is on its last legs (i.e. family connections do not necessarily guarantee you a place), the significance and potency of an Oxbridge degree is waning - i genuinely believe you can recieve an equal, if not better, education at LSE or Durham or somewhere like that, and you definitely receive a better education at Harvard or MIT etc, because they're just so rich.
The real reason most people think Oxbridge is so great is purely history and prestige. Because Oxbridge have such great alumni (which arent really so great when you consider they bought their way in... but we're not getting into that now) and is so steeped in history (wow - Bill Clinton and Charles I were in this hall where i eat dinner, which was built 600 years ago!!) people think this is amazing, but as what I term "decorative" history (stuff that has bugger all significance but people get obsessed with it like they do with furniture) becomes less significant in the modern age, Oxbridge will just be seen like the other universities nice old grandparents - they're old, they're nice enough, but you know they havent been so nice to everybody all their lives, they smell a little bit (rivers and age doesnt equal the new D&G fragrance) but you dont want to stay with them for too long, becuase they dont know how to cope with your new technology.
So I reckon if youre really into that kinda stuff, and youre one of these people who finds pomp and ceremony really inspiring (I'm not judging) then sure, Oxbridge is amazing, but in the next century it wont have as much "ooh interesting" factor as it does, and did have.