Both are 24" pigment printers.
Where the advantages for you might be certain features, for others they may not be interesting at all.
From what artists I have met, the best thing about a Z printer in the APS/PS model, PS being an embedded Adobe Postscript RIP at a very high level so printing vector work is a very simple thing to do.
It does this accepting files in rgb or CMYK in turn always using rgb to the printer. Since you create your own profiles , this is easy to apply to your art work reaching the full gamut for vector and or paint artwork. You can do this with an external rip but it's so easy to do as an embedded rip.
I don't know why or where problem reports are stronger in your findings for Mac. All the testing I did showed more problems on PC. I found very few problems with the Mac drivers throughout testing.
As far as turning the printers off. Both risk clogging if the period allows drying of the heads. Epson usually fire up with a simple cap and wipe and are ready again. The idea of HP is if you leave the printer on, there is a background daily head maintenance which keeps the heads in their optimal running state. IF you leave the printer on you'll likely never have a clog, but if you turn it off, that will put you at risk.
The HP can be slightly better at ink volume required per print but if you're not printing much it isn't something for you to worry about. The printer isn't going to use all 12 inks at any time, so the output coverage is not proportional to the number of available inks.
I would like to assume the HP is a platform that will continue to be built upon where as Epson don't have any upgrade path.
On image quality there are plus and minuses for both. Epson will outperform HP and Canon on matte. HP and Canon will outperform Epson on some images on Satin/pearl, and HP will outdo all on glossy.
Epson will be a good choice, the HP too. If you think about the PS side of the HP it may let you print artwork with an incredible ease of use, meanwhile have a repeatability for reprints that is above par.