Actually, according to Peter David, Savage Hulk is the strongest. He's the original Hulk. None of the other Hulks have ever matched the strength of good old "Hulk Smash!" Hulk. The others may have higher base strength, but when it comes to radical, exponential strength increases, Savage Hulk beats 'em all by a mile.
War Hulk had the Professor's strength, a strength increase, and magical armor that allowed him to stop Juggernaut. He cannot get stronger. War Hulk may be initially stronger, but Savage Hulk could excede him in seconds or less. None of the Hulks (not even Maestro) can match the strength of Savage Hulk. Few people in the MU can.