The 10000 is a workhorse of a machine designed to print a lot of material very fast. It is a 300 dpi based device (same as Canon and HP) and has a huge head which allows it to print faster than the 9000. Jury is still out on whether the additional black really offers anything in the printing of photographic type images, I'm inclined to think not that much unless perhaps the work is mainly black and white.
The 9000 is the traditional 360 dpi device with max resolution up to 1440x2880 in the screen/dither. It has orange and green inks which may offer better tonal gradations in some areas, although here again the difference in printing photographic images is probably not very significant. It is a less expensive printer, and to me offers better top end quality potential when printing photographs.
Don't ignore the 8000, also a 44 inch printer with all of the features of the 9000 minus the green and orange inks. Image quality side by side would be identical on nearly as the 9000 when printing photographic type images (the green and orange are designed to help prepress proofing achieve more pantone color matches).
The 8000/9000 have been around long enough now that and the reports are pretty positive in regards to missing nozzles and cleaning to indicate Epson did make improvements in this process. I've had a 9000 for 15 months and have only had to run a clean on single channel a few times. Other users have reported similar results with their new p6/7/8/9000 series printers.
There are many who are fans of HP and Canon on the forum as well and I'm sure they will offer information on the current state of those printers. All 3 brands produce excellent results. There are also dozens of threads on this forum (this question gets asked at least once a week it seems).