When I prep my encounters, I print out all the stats on one page. On that same page I have headers for each monster, their hit points, and some white space underneath. If there is a goblin hexer, 2 goblin warriors, and 2 shadow bats in an encounter, I might have some short hand like H, W1, W2, S1, S2, with their hit points written underneath each column. I track them individually. I can usually remember what's 1 and what's 2. If there are 4 or more identical monsters, I differentiate with miniatures (but that rarely happens except for minions). My damage track for each monster is also my condition tracker, so I know what conditions I start with, how much ongoing damage I'm taking, and how many saves I have to make at the end of my turn.
I use a lot of short hand. For instance if W1 was hit with the Paladin's Enfeebling Strike for 8 points of damage, I subtract the damage, and right next to it, write down "ES -2" This reminds me of the condition when it's my turn. There are typically scribbles of "ong5", "d.rad", and the like on the tracking sheet for ongoing 5 damage, been hit by dire radiance, etc.
I can move it along pretty fast since while the player is figuring out their attack and damage, I can easily locate the target on my encounter sheet, and it's not a lot of numbers to record. For marks, curse targets, quarries, bloodied, etc, we use markers under the minis so I can usually tell at a quick galnce.
I don't think I'd ever have players keeping track of monster damage. Call me old fashioned, but I like to be in charge of that stuff. As long as my players are on top of what they want to do when their turn comes around I'm happy. They do run the initiative board for me (on a good day).