I believe, that minimum resolution for jpg (in zip with eps) there is 15 megapixels (for example 3000*5000 pixels).
So at this moment I export in range 15.01 - 37.99 megapixels.
You can change DPI settings when exporting jpg or png files from Illustrator to get large files.
This resolution range works everywhere for me - except maybe for Veer, as they probably need
larger jpg for vectors.
For Shutterstock, I create small preview jpg (shorter side 500 pixels).