[Jaydelart]

There are a few ways to answer this question:
A person could choose to be wise and say there is no best martial art.
Or they could express, through personal opinion, which they believe is the best.

... And neither response would be wrong.

What we consider to be the "best" and why varies from person-to-person. It's difficult to determine who is correct or incorrect when it comes down to such things as personal preference.

When a martial artist defeats another martial artist in physical combat, he could feel that the knowledge and practice he received through training contributed to his victory and, therefore, believe that his martial art is the best. And that belief wouldn't be unjustified.

This is why there are many types of martial arts and martial artists.
There is a best martial art and there isn't, at the same time.