Which of the "A" or "S" tier killers is the easiest to learn?

I think saying hag is easy is a bit misleading. The basic concept of playing her is easy to understand but to be effective you need a good amount of game and map knowledge and need to understand some of the basic mechanics of her very well.

Plus one survivor with a flashlight can ruin your game entirely if you're inexperienced.

Freddy is probably the easiest killer in the game near the top of the tier list.

Although, I'd argue Spirit is rather easy or forgiven to learn and is the second strongest killer.

Freddy is extraordinarily basic. I'd argue he's the easiest killer to learn in all of DbD. But I also think he gets boring pretty fast (and he's no fun to play against). If you're newer to killer, he's a great starting point. If you have a decent grasp of how to play the role, I'd move on to a more exciting character instead.

Otherwise Pyramid Head, Doctor, and Billy are pretty straightforward (not sure where the community lumps them all on the tier list these days, but they certainly aren't weak). There are some neat things you can learn to do with them, but their skill floors aren't super high, so you can pick them up pretty quickly.

Though if you really only care about ranking up and not necessarily about winning, Legion still tends to cheese the emblem system quite a bit. They're like a mid-tier killer at best, but they really like to pip (sometimes even on losses).

Freddy. He’s straight forward and let’s you get closer without much effort. Trap windows, loops, and frequent paths. Upgrade and get great perks to help you (corrupt intervention let’s you set up and then start chasing, let’s them fall asleep first before chases need to happen; BBQ and Pop makes your teleport ridiculous too). Also you won’t be able to beat good survivors without putting in the time. Learn the maps, learn their loops, play survivor some to see how they hide/behave/react so you can get in their heads and start effortlessly predicting them. Most of all, don’t worry too much about rank and try to have fun. When I did this i started accidentally ranking up without even realizing it. Good luck!!

Freddy is the easiest in terms of actual being easy, IMO he is the easiest in the entire game. Spirit is fairly easy, but a bit harder than a Freddy and takes some hrs, but has more worthwhile reward as she is better. Phead is also pretty simple IMO

Three gen with hag isn't viable because playing hag u are gonna lose gens regardless of what u do just to make up time setting up traps a three gen isn't something that u should be doing unless it coincidentally happens.

Hag is definitely hard to pickup if you don't play trapp daddy.

Hey, that reminds me:

I know Trapper isn't on your list, but he can definitely preform at high ranks if you practice enough! I take any excuse to tell people to play him.

But to stay on topic, here's some info that works for hag (and trapper?) that will help you in the beginning of learning:

Never try to evenly place traps across the map, most will get wasted or be useless to you. Don't go for a 3-gen (because that's an easy wrench to throw in your plans), but instead cover a portion of the map that is easiest to control. Playing these killers will result in quick gens lost, their power is meant for snowballing and catching people off-guard. As hag, always place a trap near a hooked survivor and stay within teleport range. DO NOT CAMP, otherwise your throwing away pressure on everything else in the trial, not to mention wasting your trap. Instead, pressure the closest survivor to the hook/important gen/your web of traps.

This is not the end-all for learning hag, you'll get to a point where you know when not to place traps on hook, how to make a 'web', etc. I would recommend checking out Otzdarva's videos for a different, more in depth, explanation that is done well. This goes with every killer also!

You didn't even mention spirit. I'd recommend using either spirit or Freddy until you develop a little more skill. They're both very basic and easy to use.

Freddy but I enjoy bubba way more

This is just my opinion.... But I like to play a killer until I'm comfortable enough not needing addons or perks to get a brutal killer consistently.

I'd say that if you're having trouble against red rank survivors, it may be for a variety of reasons. Do you understand how to loop? Do you know how to run L and T walls? How long do your chases typically go for? If you are running noed, how many games would you actually get a brutal killer without it?

Would highly recommend YouTube videos from interact. Very informative killer videos.

Maybe for you but I only have fun playing as Freddy

I will say as everyone here that the answer is Freddy and Hag. But I have another opinion. Since you mentioned you felt comfortable with Legion I highly suggest you stick with him even if his power feels weak (This coming from a old Bubba main, before his rework), but I'm not saying you shouldn't play any other killers, I find it better play different killers and builds to understand the game better.

On a side note a Legion with enough ability can still go against red ranks survivors, this coming from experience in red rank matches as Legion. Another thing I highly recommend is to not take the Killer/Survivor Rank seriously since that doesn't really shows the ability of said player and forgetting about it makes the game more enjoyable (at least in my opinion)

Freddy and Spirit are the easiest but you can rank up as any killer. I have never hit red ranks yet because I still barely have any teachables unlocked and stuff, but I've successfully gotten to purple ranks just by using Plague and occasionally playing Doc and Legion.

some people may not agree but, i feel Blight is an A - Sometimes S tier killer , his power is a bit tricky to get the hang of but once you put some time into him , hes got amazing mindgame potential , his add-ons change his style/mindgames completely , Map size / RNG doesnt affect him AS much as other killers , i feel blight is quite underrated due to the skill ceilling he has , hes my go to Stomping tool at Rank 1 when survive with friends are on the loose , when the power starts to feel natural , you can expand at predicting and countering loops (he can counter shack looping quickly something not many other killers can do)

on a side note: i have a friend whom started playing DBD just prior to blight release , she decided to pick him up as her main and after putting 50-60 hours into him (she got about 150-200 hours playtime now) she managed to get to rank 1 and hang onto there easily , she even on occasion plays addonless blight without any issues , consider him , give him a try.