Why did Gfycat win? I've always wondered.

I'd bet on UI and marketing.

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.

Gfycat was promoted pretty agressively on reddit. I've never heard of MediaCrush before this thread.

They have a cooler name, I guess. It's not like MediaCrush isn't around, though.

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.