More physical exercise, useful in life, what more would you want?
PE helps physical endurance and strength in general. Later on in life, taking P.E or not will have a significant impact on your life. But not everybody is talented in music. For example, you might not become better at violin even if you practice for four years. That will just give you more despair and stress. While if you take P.E, your endurance will improve.
They are both incredibly important to the development of a human being. However I chose Music because a) I have a bias having played instruments from age 5-20, b) Music is significantly less established as a extracurricular activity free of cost (Most instruments will require significant investment of time and money in order to receive proper gains), c) most P.E. benefits can be easily achieved through city sponsored youth athletic programs, d) Its cheaper to take your kid to a park and play games.
Listening to Music can improve/boost your brain power and memory.
PE is not so useful in peacetime. I'd comment on the virtues of music, but I'd instead point those who are interested to the Book of Rites, which has an entire chapter on the nature of music.
Music! It's so relaxing and fun. It actually uses your entire brain which is nice although P. E/gym also does this. Both are also team efforts most of the time. You also would have to move your body with the music if you have that ability(if you don't have a huge instrument/sitting) to show to the audience that you are into the music and enjoy it. There is your enjoyment and some physical exercise.