ATI or Nvidia?

I have always been an Nvidia person by nature, a trait passed down to me from my dad when he gave me his old geforce 2 back in the day. Then along came my laptop and I was suitably supprised with how well it performed compared to my PC.
Since im being backed into a corner and having to upgrade my PC, getting rid of my geforce 6600 for a PCI-e, I feel the need to get some good advise so I wont be disapointed.