Love them, hate them, here goes Eeveeto Viability Ranking:
S Rank
1.

: Crit Hyperbeam goes, brrr.
2.

Best special wall, best para absorber, good status spreader, good special sweeper and freeze fisher. I mean, everyone knows what it does.
3.

Prior to the Body Slam nerf, I would easily have put him as 1st and 100% needed on any RBY Team, even in as random teams as I do. Not the case anymore. I tend to see Lax not bulky enough on either side and at the same time unable to make offensive progress because of... opposing Reflect Lax (and sometimes Chansey). Its still powerful and pretty much needed on like 95% of teams, but I don,t consider it on the level of domination it had prior to the Body Slam nerf.
4.

I am still a Big 4 believer and this is my 4th Mon. SPL win rate (highest one in the 10 most used Mons) proves me right, despite knowing that having less mirror matches might have something to do with that. Egg has Sleep, has explosion and useful resistances to electric and ground. Just enough speed to outspeed Chansey makes this Mon threatening to almost everything that it faces. Egg forces ice moves on Starmie and forces a sleeping Lax out. It has enough influency for me to be 4th best Mon. Btw, Mega Drain is his best 4th move, change my mind.
A Rank
5.

My opinion on Starmie is higher that it used to be, but I still think this Mon is overrated and needs 6 Moves to use all its potential. It dislikes para (though not as much as Tauros and Zam) and doesn,t tank and hit as much as I want it to. Still, its one of the few Mons that is faster than Tauros and the only one that switches relatively well on it. Walling Jynx and forcing Cloyster to explode are huge attributes.
6.

Everyone has this guy here and I won,t be different. As a bonus, it's the fastest Metronome user, so, its the OU Mon that is most likely to use succesfully a OHKO Move.
7.

Most dangerous Mon when Rhydon is not present.
8.

Makes Zapdos useful and is very good beyond that. Amazing para abusser and boom absorber.
9.

Best lead. Both Starmie and Zam are better Mons, but this is the most consistent and dangerous lead, the one that is likely to make the most progress early game. After those early turns it's not that good, but by then it could be enough.
B rank
10.

Zapdos check, fastest good mon, Chansey "counter" (if it has Rest + Double Kick) and more useful than Zapdos when it faces a Rhydon.
11.

Best Tauros check.
12.

Wrapper that also counters Slowbro and scares Starmie and Rhydon out. Has 2 different status and SD.
13.

Wins games by itself when it doesn,t get critted. Problem is, it often will.
14.

Very bad vs Standart teams, although it can come on Explosions surprisingly when its not lead and discourages them when it is lead. Relying on Hypnosis is never good. Its main strength its that it prevents creativity. Like 70% of the Mons that are below Gengar have huge problems with it.
C rank
15.

Strongest Blizzard, good bulk. If Chansey and Starmie are gone, it can easily sweep almost everything. Thats hard to achieve, though.
16.

Decent lead, doesn,t rely on Hypnosis as much as Gengar due to having TW too. Can be a funny sweeper with Meditate + Headbutt too.
17.

Wrapper that has troubles boosting but sweeps quite often if it manages too.
18.

Same as above, but actually threatens a lot without needing to use Fire Spin as often. Fire Blast is really strong and has 30% burn.
19.

Ignores all the Reflects, faster than Tauros, but thats it.
20.

Nice when used with Rhydon on the same team. You explode Golem on the incoming Egg or Starmie, then opponent sends the Zapdos thinking the danger is gone and you surprise him with Rhydon! ... Yes, its shaky at best, but Explosion still good.
21.

Faster and bulkier than Victreebel, so its a better SD sweeper. Don,t underestimate Venu, its good.
D rank (I won,t order starting from here)
Lapras: If Sing is what makes it viable, then its BAD. I actually don,t think that, since it also has Confuse Ray and TBolt, but Cloyster still outclasses this badly.
Kangaskhan: A mix of Tauros and Lax... with the worse parts of both.
Poliwrath: Mixed Amnesia sweeper.
Dodrio: A worse Tauros/Zapdos. It does hit pretty hard though.
Ninetales: Fire Spin goes, brr. Has more special bulk and power than Rapidash.
Rapidash: Fire Spin goes, brr. Has more Attack than Ninetales and Agility.
Flareon: Has more Attack and Special Attack than both Ninetales and Rapidash. Too slow, although it compensates it with not always needing to use Fire Spin on its moveset. Best user of Quick Attack.
Machamp: Best Fight type along with Poliwrath. Can live some Psychic and fish for para with Body Slam.
Sandslash: Beats Rhydon, Golem and Jolteon, not too bad vs rest of the Meta.
Tentacruel: Very strong Hydro Pump.
Kingler: Crabhammer user. If only the Amnesia Mons were not resistant to water... (except Snorlax).
Porygon: The best Snorlax counter, but not very useful beyond that.
Pinsir: Not a bad SD user actually, but its one of the worst Mons against Gengar
E rank
Gyarados: Not a bad mixed Mon, problem is, it won,t break anything as long as a combination of Starmie and Chansey are healthy enough.
Kadabra: Second Alakazam can be useful on some teams.
Nidoking: Ground Mixed Mon, unfortunately weak to Psychic.
Nidoqueen: Same as above, but bulkier and weaker EQs.
Omastar: An impossible to OHKO Mon that is not easy to counter without Starmie (it gest Submission for Chansey. Very strong Hydro and absorbs explosions.
Kabutops: Gets SD and Slash, still can eat some explosions, but frailer than Omastar.
Raichu: An electric that wins against grounds but gets humillated by Egg.
Electrode: An electric that gets crit Explosion... which Rhydon won,t care about.
Electabuzz: An Electric that threatens Vic with Psychic, Chansey with Submission and has no counters due to having Metronome.
Magmar: Threatens Chansey with Submission and has no Counters due to learning Metronome too.
Charizard: A fire type with extensive movepool, but does everything badly.
Mr. Mime: A Psychic type that has better chances to beat Slowbro than Zam due to learning Thunderbolt. Due to not being weak to Electric, has better match-up than Starmie vs Zapdos. It also learns Counter, so thats something.
Raticate: Super Fang user.
Clefable: Bad Chansey and Snorlax mix.
Wigglytuff: Even worse than above, but better Counter user.
Arbok: Glare + wrap. Weak to everything.
Weezing: Boomer that can take some hits, attack on special side and is faster than Egg.
Muk: Slower than Egg, but gets Megadrain for Rhydon and has 3rd strongest Boom in the game.
Parasect: Spore.
Tangela: A grass faster than Egg and not weak to Psychic. Bind user.
Onix: A meme that sometimes works with Bind + Toxic + Explosion.
Golduck: Fastest Amnesia Mon with worse problemas than Poli or Slowbro.
Vaporeon: Bulky water hard to break.
Blastoise: Water counter user. Can do some damage and take some hits.
Lickitung: SD + STAB Hyperbeam.
Dewgong: Only viable on 5 Ice Mons teams, but not a terrible Mon on its own, just outclassed.
Aerodactyl: Snorlax check that sometimes does big damage with crit Sky Attack.
Hitmonlee: Has HJK + Meditate.
Do Not Use Rank.
Beedrill: SD + Twineedle? Nah, terrible.
Butterfree: Use Egg, lol.
Venomoth: Use Egg, lol.
Scyther: Use Pinsir or Persian.
Ditto: Needs way too much support to work.
Fearow: Use Dodrio, lol.
Pidgeot: I think that its better than Fearow due to having more bulk... but use Dodrio, lol.
Arcanine: Could have been more useful if Dig was unbanned. I actually don,t think Dig and Fly are broken, any Standart team has decent odds to just outstall glicth abussers.
Golbat: Why does it have so many weaknesses?
Farfetch'd: Slash ignoring SD is sad.
Primeape: Would be pretty good if Karate Chop was Fight move.
Seadra: Bro, where is your movepool?
Seaking: Unban Horn Drill, pls.
Vileplume: Give Razor Leaf.
And that is. I think this is what RBY OU Meta is like in my head. Feel free to join the Eeveetoism, is a fun religion.