I really don't want to lose weight, so very intensive cardio might not work.
As trustin says.... The standard paradigm is that you don't play sports to get fit, you get fit to play sports.
No sport will "gain muscle"..... You do that in the gym.
For overall fitness, you would want to do a combination of things. Enough aerobic ("cardio") exercise for cardiovascular fitness, and either resistance exercise (weights) or bodyweight/calisthenic work for upper-body strength and bone health.
A sport won't gain you muscle. Just because you play football, you're not gonna automatically win muscle. They lift weights
Believe it or not but track is a great sport to do that but its not track season so maybe cross country but they are like what every sport does which is running it helps alot later in life too
Weights/lifting
Boxing
Swimming
Push ups and bench presses
racing
good question
