Average case performance vs. Worst-case guarantee

[Harsha Narayan <hnarayan () cs ucsd edu>]

Hi,
  I have this question to which I have not been able to get a conclusive
answer (I have heard different things).

  When an ISP buys a router does it want a worst-case guarantee about the
router's capabilities? Or will it buy a router which can give better
performance in the average case (it may drop some packets if the traffic
pattern changes suddenly)? Assuming both cost the same.

  Could you please give your opinion?

Harsha.