Back to ATI vs Nvidia, I tend to think they are equally ****ed or great, depending on how you look at it. Rest assured this NVidia hasn't been without its problems, like missing textures etc. that they fix up a couple of months later with driver updates. It is kind of a grass is greener on the other side sort of thing. Having used ATI and Nvidia for about 15 years, I don't find either of them have really a lot of to complain about. You'll always find the people that are not contempt at something being louder than the majority that is contempt with what they have.
What is more important, is thinking how long do you plan using the card. Will it be 6 months and then replace it for something better (and try to get some amount of money back), or will it be more like "I'll go down with this thing even if it kills me!" and use it for the next five to ten years. If going for the Hi-Fi route, you tend to lose more money, but you get the latest stuff - which might be disappointing given the price and such a short upgrade interval. If you go with the five year route, I don't recommend buying the latest or the best card. Buy instead a card from the best quarter that has already been beta tested by the early adopters, and you'll find you saved some good amount of money, grief, and still got a reasonable performance for a foreseeable future especially now that the consoles are slowing down the graphics requirements.
What it comes to shop assembled computers, I never choose brand computers, but only the parts that I want in my computer. The shops here assemble computers from the components and install all the necessary software to start it up to Windows and charge about 50€ for that job, which takes more than two hours if I did the same, hell even installing Windows 7 with the drivers seemed like an eternity. The thing is, I could have a relaxing massage for about 40 € that lasts for one hour, so this gives a perspective. And also this: the company I work in charges way more than 50€ of a single hour of my time - don't worry, I don't see much of that money myself. But I have never found bloated stuff in brand less computers, and I pretty much got all the software and exactly the software installed that I wanted in the first place.