Really? For me it is, together with Emoji One and Twitter, part of the bottom three. It looks like an embarrassed smile. Twitter's version looks even more forced or mechanical than those from FB or Apple, and Emoji One's eyes give an impression of sadness (probably because the arches of the grinning eyes aren't horizontal).

Imho, on a more 3D blob (2.5D or isometric) Google's version would be best. But as they are, Samsung offers the most convincingly, emotionally happy one, but it does not really fit the 'grinning' theme. So the HTC's example is probably best, especially in the usually small format, though it isn't the most artful one.

It's the least "grinny" one though.