Geb- the most ruthless racer out there, he used every trick in the book. Never wasted energy, and usually only made one move, a crushing one, not always at the same point either. Watch the 1996 10k, Geb used a lapped runner to set a pick on Tergat, he went took right as they came up on the lapped guy, forcing Tergat to have to wait until geb got clear to pass the lapped runner and attack, f***ing genius right there.
Viren- a shitload of finesse for this guy. He really didn't have the most brutal kick like say Yifter, but he found ways to work the race to his advantage, regardless of the pace. Always kept himself in position to control the race.
Most unpredictable: Stephen Cherono, sometimes you just don't know what this guy is gonna do. He got screwed out of the steeplechase gold in Athens, but he always runs the show and keeps it interesting.