http://www.akc.org/breeds/silky_terrier/ http://www.akc.org/breeds/yorkshire_terrier/
Silkies coats won't grow as long as a Yorkies, and less hair on the legs and clean feet. Enough hair for a topknot, but again won't grow as long as a Yorkie's. Std weight for Silkies: 9-10 lbs Yorkies: 7 lbs. Tail carriage is different. Silkies are longer, Yorkies more proportionate, height is the same at withers and hips. If I read right. Also, Yorkie topknots are dark tan at the roots, and gradually lighten toward the ends.
Nikki's got too much hair to be a Silky. He looks level (topline), do you trim his feet? If yes, another point toward Yorkiedom. Yes, his muzzle is a tad long, but his coat is way long to be a Silky, their coats follow their body outline, and should not touch the ground, as Nikki's does.
My vote: Yorkie!