I'd say get Hollow Knight first, just because you can probably get it cheaper. After you're done with that, and you like it, get Silksong. It's very unlikely if you don't like one you'll like the other or vice versa, the games are pretty similar, and they have a couple of things that could be called "polarizing" (like the map).

Unless you want to be part of the "current discussion", exploring the still new game, maybe you have friends who also play, and you can talk about things you find, then get Silksong.