Depends on how you want to structure your video as well. With my upcoming vlogs, I'll put a link to my Twitter profile and Facebook page at 1/3 and 2/3 through the video respectively, and have links to previous videos and a subscribe button at the end.
That will allow me to save space on the end card, and make the card cleaner and more concise. Making it not only more professional, but shorter and thus helping the total viewer retention rate.