Adobe Illustrator would certainly work, as would any other image editing application that you use.
Illustrator tends towards vector-based imagery, which gives you a high level of scalability- given enough scaling and detail work, you can certainly achieve similar quality as raster software.
There are some people who actually use Excel- of course, with Illustrator, you have more powerful tools.
On a more dimensionally accurate microscale, for the 24, 32, and 48 pixel scale art in RPG Maker, especially character sets or icons, you may actually find it more helpful to use a raster pixel editor, such as GraphicsGale, PyxelEdit, Asesprite, or even Grafx2. Photoshop and GIMP work here as well, but they're over equipped for pixel art, which is more of the style of the older JRPGs, as well as RPG Maker MV sprites and RPG Maker XP artwork.
Another option is to just use raster editor and paint your assets. Photoshop, GIMP, Paint Tool SAI, Clip Studio, MyPaint, and Krita are all options here. This is going to be more like what
Celianna does.