New computer? Possibly!

So me and my mom were looking around for computers and we came across one that looked pretty promising! It was a dell tower with 1 terabyte of hard drive space and 8 Gb of RAM! I also found a Nvidia graphics card that has 1 gb on it. So I'm rather excited to be getting one...if my mom decides to get it for me. The only reason why she is having regrets is that she'll never see me again, lol. The only dilemma that I'm having is the graphics card, I forgot the specific preferences and the version name, but should I go with Nvidia or ATI? As in which one is better for playing sims with all together?