These are their stories

Yes, by RP standards, that’s pretty large. But I wanted room to work. So the first GIF is 300x100. This means the GIF won’t page-stretch, but the extra width gives eyes a lot of breathing room.

The second gif is 150x100, which is just slightly wider than most 100x00 icons. You wouldn’t think that extra 50 pixels would make a difference, but it’s actually a lot easier for me to see!! (I’m not speaking for everyone here, but it is easier on my eyes personally).

This next GIF is similar to the first (wide and short), but it’s 250x100 (for if your theme doesn’t resize images that are too big and you’re using a small theme). This will be full-width on your blog only, on the dashboard it’s still pretty compact (while, again, not page-stretching).

The fourth gif I have for you is 100x125. Again, you wouldn’t think so few pixels makes any difference, but they really do. This works if you’d rather not have full-width images but don’t mind/like taller images.

For the fifth gif, the dimensions are 150x125.  That’s a total of an extra 75 pixels (much easier on the eyes), but evenly distrubuted so the GIF doesn’t seem too large to you.

This one is a lot like the fourth GIF, but slightly wider (if the previous one is just too oddly proportioned for you). It’s 115x125. It’s a little closer to an icon in orientation. 

If those don’t appeal to you, this next one is super short, but still wide enough to be visible. It’s 250x50. 

And this one is actually inspire by my computer screen (which of course is designed for readability), but (obviously) scaled down pretty reasonably. This last one is 250x156.

And, of course, if none of those inspire you, a slightly bigger GIF icon is a perfectly acceptable solution (and not as bad as people seem to make it out to be?). Here is an example of 150x150. 

And 125x125, if those extra 100 pixels are still too much for you.