James Blake has seen his share of phenoms and flame-outs during his days on the ATP tour. The American, who played his final match at the U.S. Open last month, is optimistic about the future of the sport's leading young guns.

Asked to assess the potential of four talented young players who are all under age 24—Milos Raonic, Grigor Dimitrov, Jerzy Janowicz, and Kei Nishikori—Blake told TENNIS.com that Raonic's game is the most imposing, but Dimitrov is the most exciting.

"Dimitrov has a ton of talent," said Blake, who was 0-2 lifetime against Raonic, including a loss at the 2012 U.S. Open. "Out of those four guys, I'd least like to play Raonic because of that serve... It could be a set and 3-all in the second set, you don't feel you're into the match because he's won so many free points off his serve, he's missed a lot of balls on the return game, and he hasn't given you anything to really feel like you're into the match. That to me makes it uncomfortable."

The 22-year-old Dimitrov, who beat David Ferrer in Sunday's Stockholm final to claim his first career tour title, may have the most expansive game and potential, suggests Blake.

"I think Dimitrov has a huge upside. If he stays healthy, he has a live arm, huge serve, he moves well," Blake said. "Looks like he's comfortable hitting any shot. Just a matter for him of putting it all together. If I had to say one guy that has the game that actually excites me, it's Dimitrov. Raonic is the most uncomfortable to play, but I don't get quite excited watching a guy serve 25 aces and win a match 6 and 6."

Blake, who beat Janowicz, 6-1, 7-5, in their lone professional meeting in Cincinnati last August, says the Pole's punishing serve makes him a threat, though he believes the 6'8" Janowicz plays more predictable patterns than Dimitrov or Raonic.

"Janowicz really hits the ball hard and flat. He can make a lot of balls in a row, which can give you some rhythm," Blake said. "I had success against him. I feel like he kind of sticks to patterns a little bit. I just happened to be playing well that day [I beat him]."

The 23-year-old Nishikori, who won three of four meetings with Blake, including his first ATP title in the 2008 Delray Beach final, is one of the best ball-strikers and movers among the four. But Blake suggests that the 5'10" Japanese may be more vulnerable to injuries due to his slighter stature.

"Nishikori I think is continuing to improve. It's a tougher battle for him because he's not a big guy," Blake told TENNIS.com. "I think it's tough for him to compete against really big guys, even though he hits the ball better than a lot of them, moves better than a lot of them. It's tougher for him to stay healthy and compete with the big boys."