After Valiev, I think I have to go:
Nielsen and Kirkland since they're both signed to NHL contracts, which is more than the rest of the group will likely ever see.
McKenna next because he's the most-likely of the rest to earn an NHL contract.
After that, I guess I'll go Karnaukhov then Foo just because Karnaukhov is younger and could decide to give North America another try. I don't know if playing 2 or 3 seasons with one of the worst teams in the KHL will be good for Foo's development.
Mattson was a 20 year-old freshman last season and still couldn't crack the lineup most games. He played less than half of Michigan State's games last season and still hasn't scored his first college point. I hope he's getting a good education because I don't think professional hockey is in his future.