HP z3100 or the Epson 7900 for long term use.
define long term use. If you are going to print every day, then it's probably more about features and your perception of final quality (the 8300 and 7900 are newer generation printers ). The more you print, the less issues you will have with all of these printers. If you are printing a lot, the 7900 wins because it will rarely have issues if used daily, you can buy 700ml cartridges so ink costs are less the paper feed system is fantastic and is really nice if you like to use several paper types, and if you like to print on thick papers the Epson straight through paper bath is the best design.
If you are only printing every few days and live in a dry climate, the 8300 might be less trouble on a daily basis. It also doesn't require swapping if MK/PK inks if you like printing on both matt and gloss papers. When it gets a unclearable clog it will use a spare nozzle, at some point all the spares will be used and head needs replaced. The dryer the climate and the less you run them, the faster the heads will wear out. The overall TCO probably isn't much difference over the long haul (think years) - ink for the epson or heads for the canon (which cost several hundred and there are two) ... and the canon still uses quite a bit of ink. I think the real issue is downtime getting the printer ready to run after letting it sit for several days. Here the 8300 wins because you just leave it on all the time and it's always ready to go.
I have a 9900 and only print every couple of weeks (or longer), and haven't had a clog in 6 months. But I also have a controlled room at a constant 69 degrees/45% humidity. My 4900 isn't quite as good, it often has a missing nozzle or two if I don't print something at least every 4 or 5 days. I do use it quite often, if I print every day or at least every other day I rarely see a missing nozzle.
Of course each person has their own perception of quality, I think the Epson is the best, Canon is terrific but a slight notch less and I've never liked the z3100 (I had HP setup a demo machine twice at my previous company, really wanted to make it work because of the GO, but just couldn't get the colors to look like I wanted.) the z3200 is probably better, maybe that's the one you meant?