There is really no correct answer! It all depends on what you want to do with the image once it is uploaded to google drive.
If it will only ever be viewed as you have shown on your spreadsheet, then thumbnail sized images of 128x128 px would be fine (see the thumbnail extension here). - maxheight 128 maxwidth 128
If you want to view the images at full screen size then you would need to consider a much larger image: maxheight 1080 maxwidth 1980. This will of course mean a larger file size and longer upload time (and use up more storage space of your google quota)
640 x 360 px max (aspect ratio of 1.77) would be good for general use.
As I said, it really does depend on your intended end use.
