Here's the deal. For Doom 3, it's possible for you to install the top offering from Nvidia or Ati and still not turn on all the features or run at high pixel counts.
The answer might be that you set a budget and get the highest rated card that fits that dollar.
I was wondering if anyone could recommend a good graphics card with 128mb of memory. Right now I'm using a nvidia geforce4 mx 420 with 64mb of memory. I don't think it'll run real well with doom 3, battlefield vietnam etc. What do you think? It's a dell 8200 dimension with 1gig of ram, 2.53 ghz intel processor. Thanks