Give the AC, but not the HP or saves
DMG 247 gives DMs wide latitude on what to reveal to players. This is an area where there's extraordinary variation between DMs. However, in my experience as a DM and a player, we have settled on giving only the AC. I'm also answering from a game table perspective, not an in-game perspective.
Players can usually figure out what the AC is
Players are frequently making attack rolls, which means they have a large sample size for determining AC (at least for any enemy that lasts a few rounds). For example, if the fighter misses on a 17, but the rogue hits on a 19, the players can quickly determine that the AC is at least 18. Given that this behavior is so routine, hiding the AC just adds a layer of unnecessary complication to the fight.
Reasons to hide HP and saves
The main reason to hide HP and saves is that they're never obvious to the players, which lets you keep the all-important fudge factor--if a boss is going down too quickly, or is going to die to a single spell, you can always add more HP or fudge the roll (the Legendary Resistance feature of some monsters codifies this).
The second is that some uncertainty is actually good. By giving general descriptors, players tend to be a bit more cautious and tactical in their play, which I think makes for a better game.
This is not a hard rule
If a fight is becoming a slog and we're getting bored, one of my DMs will give the HP of the remaining monsters to show how much progress we've made. Alternatively, the DM can say that we've dealt X damage but the monster is still fine, as a way to tell us that a monster is strong. You're the DM, and there's no rule that says you have to be consistent in what you give.
Players should be able to talk numbers
I think that you might be asking if the players should know how much damage they're dealing. This is a definite yes, because they should be rolling the damage dice.
Moreover, the players know the HP of their characters, and forcing the players to use descriptors instead of the numbers creates the same problem as hiding the AC--you're essentially forcing the players to create a code for a number rather than the number itself, which adds another unnecessary layer of complication.