When I think of the 'best goal' I lean towards those that are incredibly memorable. For me, Roberto Carlos' free kick was just that....once you've seen it you'll never forget it. That its never been repeated as well says it all too.
Beckham vs Greece is amazing not for the technique as there are 20+ comparable free kicks a year but because of the pressure.
So naturally Bergkamp vs Newcastle trumps Bergkamp vs Argentina because the latter has been replicated by others, and even Bergkamp in other games.
Other goals that stand out: Ronaldinho's two goal haul vs Madrid, Ronaldinho vs Chelsea, Seedorf's long range blast, Essien vs Arsenal, Di Canio vs Wimbeldon and: