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.
Started Castlevania: Harmony of Dissonance, after I finished Circle of the Moon last week. It looks and sounds worse than CotM, but it's a lot better than that game, because it doesn't play like ass.
Some other meh stuff is still there, like the game is kinda easy, and exploring the map is an absolute chore for the first half (maybe two thirds), until you finally get the means to open up all the blocked paths and get access to proper teleporters. Still better than double-tap to sprint though.
I haven't finished the game yet, I might be near the end, but didn't make it before Hollow Knight: Silksong, which I gotta play first.