HP isn't really that great, but many of our customers like the way the large printers print. Canon has great quality and plug-ins that assist with the printing from the programs. Unlike Epson, Canon has replaceable 2 printheads in the larger models (24" & up). Epson print heads need to be replaced by an authorized service center; which, can possibly cost as much as the printer or more (depends on the issue). Most of the Epson inks with the printer are starter set while Canon ships a full set with the 44" and larger (normally a better savings upfront). Epson and Canon are pretty reliable both ways and do great jobs on the printing. Epsons feeding is straight thru from the top and Canon feed from the bottom up and around to the front (but this isn't much of a problem with most medias still).
As far as programs to make sure the color is accurate, Epson has their RIP software and Canon has the programs that work the about the same way.
If you need to have the colors match up better than the programs, there is a hardware called ColorMunki that calibrates the screen to make it match the prints.