In high school, I didn't always look like a model student. I missed countless days of school for national/international fencing tournaments and sometimes cut classes to study for exams in others. I wasn't involved in any clubs due to my rigorous training schedule. I didn't have many friends because I didn't have enough time to hang out with them. To my peers, I probably looked like a human belly flop with low participation marks and horrible social status. Was it worth it to miss out on all the fun?
I felt like it was worth it. Being good at a sport was a confidence-booster, and being so committed to it enforced personal characteristics like good time-management skills, working hard, and meeting deadlines. I was excused for my absences by writing to teachers the week before a tournament and completing extra assignments to make up for missed class days. My grades and test scores looked solid on paper, and I didn't feel like I was missing out by not being in a high school club. If colleges were interested in me for my strong athletic performance, then I didn't see the necessity of taking on more obligations than I could handle. Several adults also told me that hiring managers seek out student athletes for their ability to balance time and maintain a strong work ethic. With that in mind, I didn't have to join the same race as my other friends who were trying to enter as many Model UNs or Science Fairs as they could handle.
On that note, I'm definitely not trying to say that being an avid participant in every Model UN or Science Fair is a bad thing. On the contrary, it's a great thing that I'd recommend to students, but it just wasn't the high school life I was familiar with. I had friends who competed in national BioGenius science competitions or conducted their own research at local university research labs twenty minutes away from our hometown (the students at my high school all had a similar overachiever mentality, and with everyone trying to be the best, it was harder to actually be the best, which is why our school was non-ranking and didn't crown valedictorians or salutatorians). Everyone was scrambling to win a high school hack-a-thon or Chemistry Olympiad, but just because everyone had the same levels of strong experience, that didn't mean they were less exceptional. They all had great resumes, and that was that. My opinion is that pursuing an extracurricular as passionately as possible is the best way to stand out to colleges. It doesn't have to be a sport, but it helps to know what activities colleges value and what activities make you happy.