I've been to separate presentations put on by the three manufacturers to demonstrate their capabilities. I truely believe that at that level of printer, it is more of a matter of personal preference than capabilities. All three manufactures printers will produce beautiful output.
It's similar to asking which DSLR takes better pictures Nikon, Canon, Fuji, or Sony. It depends just as much on the user and his/her ability to utilize the features and capabilities.
Also remember that it's not just the printer, but also the paper that will effect the final output.