With how resting seems to be presented in this game, I prefer spell slots. I don't want to see combat turn into a nova fest.
I also think most optional rule variants in general should be gone from the game. They are great for pen and paper because each table's game is played in isolation, and the DM can tailor a campaign for a table. BG3 needs to develop and balance a single, clean experience for hundreds of thousands of players. Subclasses, feats, and other character building options are fine, but changes to core rules are going to get in the way of that.
