I notice that the Epson 7900 print head has 3600 nozzles and the two Canon print heads have 30,720 nozzles combined, so this may affect the price of the heads. Whereas the single head for the 10 color Canon Pro 9500 has 7680 nozzles and sells for around $125.00
This difference is simply due to the different technology ... advanced bubble-jet for the Canon, and Piezo-electric for the Epson. Epson nozzles and heads are designed to last the life of the machine. If a nozzle clogs, ink is used to clear and restore it. Nozzles on the Canon (and HP) will wear/clog over time, and the printer monitors it. While some attempt is made to unclog nozzles, it is less aggressive, and instead the printer will remap that nozzle to a "spare", of which there are thousands. Theoretically all spare nozzles can get used, which then means the only way to resolve the problem is to replace the head. I believe the Canon heads are more expensive because they contain 1/2 of the colors (6) where as HP's each are for just 2. I've heard but cannot verify that HP includes fewer spare nozzles in their heads to keep costs down ... if this is true it may mean HP's might need replaced sooner. However, both printers heads usually require substantial use before replacement becomes necessary, and in fact those printing their own prints may never need to replace the heads.
Both technologies seem to work, especially now that Epson clogging is substantially less than it's original printers. One advantage of the Epson technology is accuracy of dot placement. Since it always uses the exact same nozzle, and by using some new advanced materials in the 11880/7900/9900 heads, Epson claims they can control the placement of dots much more precisely than other technologies, which allows them to used more advanced screening algorithms.
As far as which printer, I am somewhat biased. I tried a z3100 extensively for several weeks on 2 different occasions, sent it back and stayed with my 9800 ... sorry but output just wasn't really much better. The onboard spectro has no appeal to me ... I would rather take full control of that process using my external tools. I also tried an ipf5000 which I didn't like at all, and I didn't use MK ink enough to justify the printer
More recently I have been totally delighted with output from my 3800, as well as my 11880. Clogging on both of those printers is really a non issue. When the ipf6100 was introduced, Canon sent me one, and I have used it for over a year with great success. MAJOR improvements over the 5000 I had. Output is terrific, although there are some subtle gradations and details the 11880 seems to handle better ... but I'll admit its difficult to see and a subjective opinion.
I have just replaced the 6100 (which I have no problems recommending to anyone) with an Epson 7900, and personally I feel build quality, dithering and screening technology, inkset and gamut, as well as ease of use and flexibility of handling of material, this is best printer I've ever used. Fast, quiet, incredible output, a terrific new roll paper system that doesn't use a spindle ... this is the best printer I've ever owned or used.
I have not used a z3200 (and won't), so if they have solved their red problem as well as some of their other concerns (which from early reports it appears they have), then it perhaps could be a contender for someone just buying a printer. Again, the spectro to me is something I would not like having to pay for ... I just want more control and ability to use more advanced targets.