Many spermatozoa, but just one ovulum
I think the asymmetry allows for a stronger selection process.  Sperm competition is a powerful force in evolution.  

This is useful since sperm vary wildly in quality - for healthy human males only 50% might not be normally motile. Other animals can have a higher percentage, but there are always a significant number of floaters... This means that the fertilization via sperm takes out a lot of the less functional sperm.  Since these are in many cases the same genes we use as diploid organisms later, sperm competition really tames a lot of problems which might be produced in meiosis.  

Many animals have multiple mating events from multiple males at just about the same time - when the female is in heat.  This gives a larger role for sperm competition - literally different sires are competing as sperm to fertilize the egg.  

In females it is a different process of choosing the cells.  Ova are mostly eliminated in women by the time they reach reproductive age.  I think that this is not well understood biologically... references are hard to find.  

The differences in the morphology and roles of the gametes, which goes back to the most primitive of animals has a strong role in selection of healthy offspring through a diverse set of mechanical and biochemical conditions experienced during fertilization. 

Added Note: I ran across this reference for how ova are selected for presentation by the ovaries.  Its not really a review, but maybe a lead reference on how selection works in the female reproductive system - its also picky:


  In mammals, ovarian folliculogenesis is a process regulated by complex networks composed of various endocrine, paracrine and autocrine factors that interact coordinately.


Its no cake walk to being an egg either...