Ultimately your decision to pursue a given major will be your decision. Take the advice of many, weigh the pros and the cons and then make the best informed decision that you can. With that being said, I will offer you my $0.02.

If it were me, and I had the opportunity to pursue a degree and fly, then I would most certainly pursue a degree outside of aviation. Why? One word - diversification.

What would I study? I would make a list of everything that interests me which could possibly be studied. Next, I would see how feasible those skills would assist me in the real world. i.e., do I have a truly marketable skill or just a piece of paper?

Many will tell you to get a degree outside of aviation solely as a back-up in case flying does not work out. I will challenge you with this thought. In the event that it will work out, would it be nice/beneficial to have another skill that you can practice in addition to flying? Think about the opportunity(ies) that may abound for you on your days off.

Again, the latter part of my post is just my thoughts and opinion, so take it for what it is worth. Just be sure to put much thought into whatever decision you decide to make.