Personally, ATI (AMD now) have the better image quality.
ATI's image quality is so vibrant and unbelievably colourful, whereas nVidia...they're just that - nVidia..they've got the technology, and they like to flaunt it..but they don't have the love
I highly recommend ATI...the only reason I don't have one right now, is due tothe fact of the deal I got this video card for - it was unbeatable!
Also, check this website out -
www.staticice.com.au - you enter the name of the part you want, and it searches almost all online shops and returns the current prices of that part you requested.
That being said - AusPC Market, is more expensive then alot of places - but the customer service is without flaw - next day delivery anywhere in australia (unless it's country road) and all the prices include shipping & handeling.