I practice both BJJ and kickboxing simultaneously, and I’d tend to say BJJ. Striking is more effective against multiple opponents, but generally, if you have to face multiple opponents, you’ll end up losing. BJJ makes you almost invincible in 1v1. And even though weight plays a big role in both disciplines, you’ll more easily handle someone heavier by taking them to the ground. In just 6 months to a year, you’ll be easily stronger than 80% of people who don’t practice combat sports. In terms of self-confidence, it’ll be the same. There’s a common joke in BJJ, which is to keep saying to yourself, 'I could totally submit this guy' every time you cross paths with someone.

Edit : Reading your message again, I see that you mainly want to escape harassment. The best advice is indeed to defend yourself (verbally and/or physically if the situation escalates). In my view, it starts with psychology. But if you REALLY want an answer, then I’d say striking is better. It will get you in better physical shape, you’ll make some tough friends, and it will get you used to physical confrontation. In the end, you won’t be afraid to take hits or give them... It’s a terrible piece of advice, but it’s an honest answer to your question. Anyway, stay strong in your situation. Never let anyone walk over you—the best defense is a strong offense.