I use GitHub because it's the coolest kid on the block for open source. Searching for repos you need/want is easy.
Especially with the apache foundation moving their workloads to them, unlimited private repos, and a package registry on the way, they are becoming the one stop shop for open source needs.
I'm curious to see how the GitHub Sponsors(patreon for developers) plays out, and what it'll do for open source. Hopefully, they design it in a way where it's not abused by big tech to "plant" developers that look like they're building open source when they're actually building proprietary tools.