The decision is up to you, but this is why I chose 24px for GemSet:
The minimum resolution for vanilla DF is 80x25 tiles. And for tiles, horizontal resolution is the only limiting factor. If you want to know the maximum tile size someone can fit on their screen, you take their horizontal resolution and divide it by 80. For my monitor, that would be 1600px / 80 = 20px tiles. But...My monitor resolution isn't the most common one. After doing some research (a.k.a. Googling "Most common screen resolutions") I eventually concluded that 1920px is one of the most common resolutions for gamers. Which is 1920px / 80 = 24px tiles. 1920px is also the resolution for 1080p and if you double it, you get 4k resolution.
This means that even though I can't view GemSet myself, a vast majority of people can and those with 4k monitors could use the 48px version. 32px isn't as good an idea IMO because it's way too big for 1920px users and way too small for 4k users. Also, remember that as you raise the resolution, it exponentially increases the amount of work that goes into drawing tiles. I started GemSet on
January 1st, 2015 (ahaha so ugly) and did not complete the creature graphics until May 15, 2015. Not to mention, I had experience with pixel art, drew it in 24px, used a really simple style and dedicated almost all of my free time to working on it. For someone with less pixel art experience, drawing in 32px, using a detailed style and having other work to do, you could be working on this tileset for almost a year!
*Not a pixel artist.
They are seriously amazing. I know that more people use 24x resolutions, but 32x is nicer to see obviously. Your choice. Either one can be up/downscaled with various quality losses.
He's not a pixel artist, but he's an incredibly-talented
commercial illustrator.
I've seen this happen so many times before...Most people with digital art experience draw really mediocre pixel art when they're starting out, but after a month of work they're better than most dedicated pixel artists out there. Man, I remember seeing this digital artist post some Japanese art on /r/pixelart.
This is what he looked like when he started out and
this is how good he got after a month of work. It's crazy, man.