Question: What kind of person are you looking for? Someone strong? Someone clever? Answer: It will have to be someone brave, like a knight.

Was knight spelled knight because it is a type of fighter from the middle ages who are often portrayed as brave now a days. Neither sentence is more common it depends on the context around it though which one would be correct.

The actual sentence would be, "Someone will have to be brave, like a knight.", which is not very common, but can be understood by pretty much most people.