Which is better Norton or Kaspersky anti virus?

I am planning to buy an anti-virus but I am confused ..I have heard norton slows down your pc, is it true? I want anti-virus which will detect all kind of spy-wares and sometimes I feel that I have been key-logged, I feel that everything I type gets recorded in someone else’s PC which anti virus & which version of the anti virus will take care of this problem…I have avg free edition right now but I am not satisfied with it

I need answers fast because I am planning to buy it tomorrow