I'd like about as slow healing as possible (very slow mundane healing, very expensive consumables, with limited spell based healing being the workhorse). A big advantage that this (which is the 1e/2e system) has is that it opens up a huge amount of adventure design room. If PCs can't even dream of starting every encounter at full HP, they'll break down and accept adventuring while injured, making attrition a real thing. This in turn allows for non set-piece, balls-to-the-walls encounter to be worth playing through.
While you could run on mundane healing, that has the huge problem that damage isn't uniformly distributed. Spells can preferentially targeted at PCs who took unluckily large amounts of damage, keeping all the PCs going concerns even with tightly limited amounts of healing.
The really big advantage? Player failure WITHOUT TPK becomes possible/reasonably straightforward. With fast recovery, winning a fight ugly is just as good as winning it cleanly. The only way to lose is to lose a fight. Given that PCs never surrender*, this means death. Without fast recovery, it costs more resources, and eventually you run out, and say "nope, we don't do another room", while still alive. The existence of consumables (that you don't want to use! expensive!) provides an emergency reserve if a fight starts to go bad when you pushed a bit too far.
*Yes yes, you know of one case where the PCs did, in fact, surrender. That's nice.