Which is better karate or martial arts?

Which is better karate or martial arts?
Which is "better" is always a matter of opinion. There can be no distinction between the two options presented as they are the same thing.

"Martial Art" is a general heading that covers all methods of combat, and most experts distinguish it as a training of the warriors character and philosophy of life with moral codes as well as combative skills. "Karate" is sub-heading which has been used to identify several different entities including Chinese hand fighting ("Tang Hand" of the Tang Dynasty), and the Japanese as well as Okinawan versions as well as a generic term to refer to all methods of unarmed combat.

Even when comparing one particular Martial Art system, methodology, or curriculum to another, there is no way to determine one being "better" except as opinion and personal preference. The effectiveness of any Martial Art is dependent upon the quality of instruction, the dedication of the student, and the correct application in real-life self defense. A person may be really good in a specific system and another may be bad in another system. It doesn't mean one system is better than the other.