Which file do I upload?

I have 2 files that are very similar, one is the original, the other is nearly 30 pixels taller and completes the full picture.

Neither has any noticeable artifacts, and they are saved as .tif files however I can make a .png of whichever should be uploaded in the event that .tif isn't supported.

By "similar", do you mean there are notable differences between the two or simply that they're the exact same picture with a size difference?

If it's the first case, you could upload both and make the slightly bigger one a parent of the original; otherwise, uploading the biggest one is your best bet.