I agree that いらっしゃいませ fits the GIF best. Also, いらっしゃいませ fits the movement of the mouth best, I think.
Welcome translates to いらっしゃいませ and to ようこそ, and while ようこそ seems more appropriate for a welcome into a community, the GIF obviously is about coming into a store. This GIF with the message いらっしゃいませ conveys to me a feeling of ‘welcome, I am here to help’, which is a nice message to send to a new member.