I voted Caesar. Though Alexander and Julius both were excellent commanders, tacticians,... I had to chose Caesar over Alexander.

They both had the best troops of their time at their disposal and fought mostly against inferior yet enormous hordes of adversaries.
But unlike Alexander, Caesar had a long way to go before he was able to command his legions whilst Alex succeeded his father and inherited a fine war-machine.
Alexander fought mostly against the enormous armies of the Persian empire and while he was very apt in destroying that war machine and leaving a hellenistic legacy, I believe the Persian soldiers were lesser warriors than the Gauls Caesar's Romans faced. Also, while Alexander showed he could overcome any foe and any army, he had problems with the Indian kingdoms, Caesar could destroy any army fielded against him. Alexander's greatest flaw imo was that he didn't leave a kingdom. He set no base for a dynasty and left his great empire to be devoured among his 'finest' generals. Caesar begun an empire which August finished.