Edited: Your tilesets are currently useful for full games since they tend to align in terms of resolution & palette. I vote 8x8 base with 16x16 groups, like https://samvieten.itch.io/metroidvania-pixelart-tileset-biomes, so your various tilesets will continue to be compatible with one another.
Viewing post in Rogue Noir 2.0 | Sizes & Ideas comments
Thanks, I should have said "will be if they continue" - basically my vote is for you to continue with consistent palettes & tile sizes so your Rogue Noir 2.0 will also be compatible with the work you've already published.
16x16 seems to be a popular vote here, but I'd point out that 8x8 sets can include 16x16 groups (which can be directly used in 16x16 tilemaps), but if the smallest tile is 16x16, then the tileset now requires 16px tilemaps to be effective. The way you've used 8x8 with 16x16 block groups so far is ideal.