What application platform should I use?

I’m a high schooler and am about to start applying to schools in August. UPenn’s my first choice and I’m applying ed. I’ve just assumed I’d use common app but now I don’t know. Someone on Reddit was talking about rankings on quest bridge and how if you match with a college you’re committed even if it’s your 10th choice. I’ve also heard it’s more competitive, but that it’s the only platform where you can apply rd if ed doesn’t work out. I’m just wondering what platform you all applied through?