Go for the 44" size. Going with a 24" will lead to a life of semi-sorrow, which I know from having suffered that fate myself. Way back when I was quite certain I would never need to make prints more than 24" on the short dimension. But as soon as I saw those gorgeous 24 x whatevers, I knew there was a special mojo to large prints and I immediately wanted more. Now, more than half my prints are larger than 24" and those are my most profitable and readily sold sizes.
Have been extremely happy with my 8300, which has served me well almost every day for last 1000+ days and 34,000+ square feet with no significant down time except the 1/2 hour it takes to occasionally replace and calibrate a printhead, which can be easily done without tools. If you're printing a lot almost every one of your printheads will wind up being replaced in-warranty, but even if you're an infrequent printer the lack of having to deal with head clogs will more than make up for the cost of out-of-warranty printheads. For the most part it's as reliable as a refrigerator, I just send it prints without even bothering to do nozzle checks or align the paper, and it just prints them and handles spare nozzle swap-outs all by itself until there are no more nozzles to swap, which usually takes about 10 to 11 months of the 12 month head warranty with heavy use. Heads are warranted separate from the printer, so your most common problem, which is printhead replacements, may be coverered by warranty for the life of the rest of the printer. It's indifferent to humidity, and prints just as well at 60F as it does at 80F, which is the range of temperatures possible in my printing room. Maintenance tanks seem to last forever, I went all of 2014 on the same maintenance tank.
There are few issues that may or may not affect you: certain canvas media can not be coated with paint rollers due to ink smearing, and for very heavy media you may been to burn about 8" media when the printer has stood idle for more than a few hours, in order to prevent head strikes from the curl in the media path just ahead of the print heads. That problem may be limited to high altitude installations where "Maximum Suction" is more like "Medium Suction" at sea level, such as my 6000ft high printing location. And printing on sheets is much less convenient than with Epsons, and it can not print on rigid sheets at all, which is possible but clumsy with the Epsons.
I print most of my work at 300 dpi, which makes for very fast printing and gives me prints that seem mostly limited by the file resolution. I am told the 8400 is just as fast at 600 dpi.