With Generalship it all depends on a variety of circumstances, that going by not losing a battle/campaign is a flawed way to rank a general. You could still be a good general despite losing several battles, Anyway here is my list:
1 Oda Nobunaga: had a combination of brutality,boldness and a willingness to adapt and use technology. Nobunaga pretty much was able to come from nearly being subdued by Imagawa Yoshimoto, to conquering most of Honshu.
2 Paul von Lettow-Vorbeck: Held off the British Empire and managed to tie up most of the Allied forces in East Africa, despite being heavily out numbered, and with little to no support from Germany.
3 Vlad Dracula Basarab: Despite being outnumbered still engaged in brutal defensive warfare with one the strongest powers in the world and win.
4 Cao Cao: laid the foundations of the state Wei, and went from a small army comprised of his family members, to controlling northern China. Cao Cao was a person who was good at leading, but had just as capable subordinates.
5 Hao Zhao: a general of the state of Wei during the Three Kingdoms period of China who managed to defeat Zhuge Liang one of the most famous generals of the era in at the siege of Chencang despite being outnumbered 100-1.