I think it's probably too early to call Gfycat the "winner", and I don't necessarily see why there isn't room for multiple providers. There's no reason image sharing needs to be a "winner-take-all" game; in fact, it behooves everyone if there is a bit of diversity in the space. I understand that reddit (the organization, not only the community) likes to aggressively favor single image sharing vendors, and that sucks, but surely there are other places where such a site can find usage.
The player is very unobtrusive and minimalist, and simple things like pronounceable random names probably appeal to the user.
Also, features that are well-known to heavy reddit users (such as easily resizeable videos) only helped with the word-of-mouth.