Is there an image file that is preferable when uploading pictures to assets?

Tango Reserve recommends a width of 2560 pixels, which will look best on monitors 2560 pixels wide or less. If the resolution of an image is lower than the resolution of the monitor used to view it, the image may appear blurry or pixelated. 

Check out this article for more information on Reserve Images:

 https://tangoanalytics.zendesk.com/hc/en-us/articles/9608670037779-Reserve-Image-Guidelines