First and foremost: the ECs are FOR YOU, not for the college which your or your parents chose for bragging rights, not for your teachers to put on the school’s brochure, but for you. It is your chance to engage in something that you love, to accomplish something about which to be proud, to push you ideas, to help a cause which is important to you, etc.
Your choice of ECs should be determined not by “will the Ivies like this EC?”, but by " will I be proud of what I did, no matter what college I attend?".
Of course, for college which care about their “brand”, the bigger the award, the better, international recognition is better than national, etc. However, this does not mean that international recognition means “a sure thing”, nor does it mean that local recognition “isn’t good enough”. Few applicants actually receive even stats-level recognition, so you are rarely in a position of “I’m the only one who didn’t win a state competition”, despite the profiles you may see on CC. Long-term a serious engagement in a couple of extracurricular activities, and perhaps exploring another one or two is what AOs are looking for.
Moreover, recognition at that level is usually only possible in ECs which involve competitions, but practically impossible for ECs which are not really competitive, like dance. Of course, EC which involve a lot of subjective judgement, like fine arts and performing arts, it’s even more difficult. Luckily, these ECs are generally good for most colleges which put emphasis on ECs.
So, while “I have two national medals in science competitions, and am president of our physics club” looks great, so does " I spend 10 hours a week working with Meals On Wheels, and have been working in theater crew since freshman year, and have been in charge of set design since sophomore year, and I have been playing the clarinet since 6th grade, and have been first clarinet for the past year".
Here is the thing - when you engage in an activity about which you feel strongly, for which you have a passion, you will be seriously engaged, and likely become a leader. “Become a leader”, mind you, which is not always the same as “hold a leadership position”.
Now, while some people say “to get accepted into a certain major, you need to have ECs in that general field”. This is also backwards. The point isn’t to do math competitions so that you can attend a selective CS program. The point is that, if you are the sort of person who loves math, and is generally good at it, you will be in math club, you will participate in the competitions, and you will likely get awards. This also says that majoring in CS is a good idea for you.
Choose your ECs based on these things:
-Does it interest you? other wise you’ll find that spending much time doing it is a chore. It’s even better if you have real passion for it, if you truly care about the activity/topic/etc, enjoy accomplishing things in it, etc.
- Does it challenge you? Just doing stuff which is easy, where you stay in your comfort zone doesn't help you grow as a person, which is the entire purpose of ECs.
- Can you actually accomplish something while doing it? You may really enjoy playing computer games, and find dome of them challenging, but getting the highest player score in the city isn't really a serious accomplishment.It needs to be meaningful.
Do not choose ECs because “T-20 colleges like them”. That’s sad, really - spending all of this time and energy trying doing something you don’t really care about, for a 7% chance at attending a college which you chose just so you can brag about it to the few people who actually care.
As for what’s considered “stellar” ECs? For colleges like Harvard, the more the ECs can help their “brand”, the better. So, the higher the level of recognition, the better. Of course, since few people achieve this, they will generally be satisfied with people who have done ECs which demonstrate the ability to attract attention, preferable positive attention.