Everyone who answered with either lion or panther is a straight up ignorant, moronic idiot. Size, weight and other qualities DO NOT affect anything. Why? Because these two animals have no natural instinct to fight. In fact, most wild animals would rather do other things than fight. Felines especially! It must take an uneducated fool to ask or answer this question without proper knowledge of wild animals. Big cats such as lions and panthers are so unlikely to attack each other. Its the last thing they want to do. Most wild animals will only fight with animals within its own species.
Although you can't force a fight between these two *wild* animals, there are natural occurrences where they must fight because its survival. For example if there was a shortage of food, a pride of lions might scare of a panther from a carcass. No fights involved. There are a few more situations where a "fight" would be necessary for survival.
Lions and black panthers normally do not live in the same places. But if one of them were to encounter the other one, they would both just turn around and walk away. Why can't people understand that? No battle goes on between any animal in general except for situations like killing prey. All of these "Who would win" questions are so annoying. I'm guessing they come from uneducated 12 year olds who simply have nothing better to do than to imagine two COMPLETELY different animals battling each other.
Lion. Its just no contest. A black panther might way 70kg, a male lion would weigh over 200kg. It would be like a 6"2 grown man against a 9 year old that's the kind of size difference between the two.
Male lion
Male African(or Asiatic) Lion.
Male lion pretty easily
Lion
Who
