Seriously. It amazes me how Evernote can be successful sometimes.
This is such a simple feature that should have been executed 10 years ago! Of course you need to be able to chose what thumbnail you want the note to show. It has such great value for the USER (your paying customers), and still you don’t do it!!? What is the reasoning behind not executing on this?
Also, is it right that the thumbnail changes based on size? If you create a note with only one image, I believe that image will remain the thumbnail no matter how many other pictures/formats you add afterwards, right? So a work-around is, if you know what thumbnail you want, to create a note with only that thumbnail and then add the rest of the content after saving it. But seriously, just fix it already!
I have used Evernote since 2011 and paying customer most of the years. I would definitely recommend the product if you were just more customer-centric. At least explain why you haven’t/don’t want to make it possible to change thumbnail.