I like to split the youngsters into a few tiers.
First tier is Nishikori and Raonic, who have already broken through and have shown they are not just hype. They are hard workers, and it's just a matter of time before these guys are top 10 players. I think Nishikori is a potential slam winner, but I haven't seen that in Raonic yet.
2nd tier would be Tomic and Janowicz. They have had some great wins, but can't seem to string together good performances consistantly yet like Nishikori and Raonic can. Also seems like they haven't really matured mentally yet, and when they do they will be that more lethal. However, it's still unclear if they will ever truly utilize their potential.
3rd tier you have Dimitrov, Harrison and Goffin. They have occasional flashes of brilliance but haven't had any really impressive wins yet. Not as naturally talented as Tomic/Janowicz, it's unclear if they will ever be more than top 20-30 players.
4th tier would be the names that you've heard occasionally but haven't really done anything worth talking about yet. People like Steve Johnson, Kudla, Jack Sock, etc.
I am a fan of Federer, Nadal, Djokovic and Murray. Yes, that's possible.