This question is a bit of a riddle or a play on words. It's likely referring to a situation where a man is comparing his wife to a bed, implying she is very comfortable and enjoyable to be around.
The answer, then, is the first best bed to his wife. This answer plays on the idea that the man's wife is the best thing in his life, and therefore, anything else that could be considered "best" would have to come after her.
This type of question is often used humorously to highlight a person's strong affection for their partner.
