If you are at all concerned about cost, the MP600 would get my vote hands down. They both have 9600 dpi which is going to make the most difference in photo quality. I can tell a difference between 9600 dpi and HP's 4800 dpi. I cannot, however, tell a difference between the printers with light cyan and light magenta, like the 960, and those without, like the 600.
The main difference between the two is features. If all you are interested in is print quality, then save your money.