Disclaimer: The way that my ranking systems are set up is based specifically off of my personal opinion and their utility from a usage perspective in a traditional campaign setting. I view a traditional campaign as being one part roleplaying, two parts adventure and two parts combat. While your ability to roleplay based upon a particular selection will be taken into consideration, I always find that in DnD you can justify roleplaying specific ways despite your subclass. Some people may call that power gaming, but the point of DnD is to be challenged, have fun and stay alive despite the odds. If you die because you want to be cute and gimp yourself, you just failed on two of those. These ranks are also heavily weighted to abilities that are granted prior to level 15 as the vast majority of campaigns end before you reach that point.
The paladin is a generally amazing class and, in my opinion, easily one of the best in 5e. With how powerful the base class is, you simply can not go wrong by picking any of the oaths available. They each add a little bit of flair, some spells (some of which are not available to you otherwise) and extra abilities. While you're not necessarily a spell caster and you are more likely to just use your spells for Divine Smite, some utility spells that are added by certain Oaths are particularly helpful. You select this Sacred Oath at level 3 and gain extra features at levels 7, 15 and 20. This guide will mostly take into consideration the perks that you gain at level 3 and 7; however, as most campaigns do not make it to level 15 those will be mostly ignored.
8: Oath of Devotion
You are fulfilling the archetype of the paladin but not much else.
The good news is, you are a paladin and they are awesome. The bad news is, you do not feel particularly special by picking this. Turn the Unholy functionally grants you the Cleric's basic Turn Undead ability which is interesting but a bit underwhelming. Your spells are mostly already available to you and nothing truly shines in the list. The most exceptional perk you get is at level 15 with Purity of Spirit which grants you the effects of protection from evil and good permanently, but this comes so late as to be a non-issue in most campaigns.
7: Oath of Conquest
You have very lofty goals that help greatly with roleplaying but your perks do not add much.
The spells here are mostly mundane but Conquering Presence, your Channel Divinity, can be very powerful. You can strike fear into anyone you can see within 30 feet of you which may entirely alter the course of a battle. If you roleplay this as a psychopath that wants nothing but power and to conquer the world and strike fear into the heart of your enemies, you have a solid character. Aura of Conquest allows you to stop anyone that is frightened in their tracks instead of making them run around, which takes away the worst part of the frightened state in 5e.
6: Oath of Redemption
Possibly a bit too pacifistic for D&D, hippie. Can't we all just get along?
This Sacred Oath is very peculiar and interesting. It makes very little sense in certain campaigns where you will have irredeemable enemies such as hordes of undead or unrepentent fiends attacking you, but it can be a wonderful fit in a less violent campaign. It is a fascinating concept from a roleplaying perspective that you want to give peace a chance and you think your enemies can be innocent.
Most of the spells that you gain by choosing this are lackluster, but you gain access to the ever powerful counterspell. The value of this spell can not be over stated. If you are in a conversation heavy campaign Emissary of Peace gives you +5 to charisma for 10 minutes which is very powerful. If that fails, you can use Rebuke the Violent which causes damage to an enemy in the same amount that they just caused to a companion. You can also choose to take damage that would otherwise hurt your companions and your level 15 ability gives you low level regeneration every round. This is a wonderful choice for a roleplay heavy campaign but still a good choice for a combat heavy campaign.
5: Oath of Glory
You are a megalomaniac but everyone will probably love you for it. Your DM certainly will.
You want personal glory, or perhaps glory for your party, which makes you an ideal adventurer for any DM. Right off the bat that makes me like this Oath. The good news is, it adds more than that. You gain access to the ever valuable haste spell along with freedom of movement, but you also get guiding bolt at level 3 which makes you a viable ranged damage dealer on top of being a tank.
Inspiring Smite is very interesting as you functionally heal your party members in any way you want, but 2d8+ your class level will have diminishing returns later on. Early game this can be a huge life saver, though. You get Glorious Defense late at level 15, but it gives you the ability to add AC to your companions and if the attack misses, you get a free attack against that enemy. Nothing to scoff at here.
4: Oath of the Ancients
You have a direct connection with nature. Likely from hugging too many trees. Thankfully, nature returns the hugs with some powerful abilities.
Unfortunately, unless you are in a fey or fiend heavy campaign one of your Channel Divinity is not particularly useful. Nature's Wrath has limited use as well, but at least you get to ensnare an enemy. Then again, it costs a full action, so it may be better just to kill them. With that being said, this Oath does come with ensnaring strike, misty step, speak with animals, ice storm and a ton of roleplaying flair. You are essentially a paladin masquerading as a druid. A vow to nature.
The best part of this Sacred Oath is Aura of Warding at level 7 which gives you and any friendly creatures within 10 feet of you resistance to damage from spells. This can very often be the difference between life and death. This extends to 30 feet much later. Undying Sentinel at level 15 allows you to basically raise dead yourself for free once per long rest when, instead of going down to 0 hit points, you can go to 1. This is a very under rated Oath in my opinion between the great roleplay opportunities, interesting spell selection and powerful perks.
3: Oath of Vengeance
Your name may be Inigo Montoya, but even if it is not, you still shall have your revenge.
You are a single target damage dealing machine and the bane of any Big Bad Evil Guy (BBEG). You actually get two solid Channel Divinity options, but one simply outshines the other in most circumstances. Abjure enemy allow you to frighten and completely stop an enemy in its place. What could be better than that? Gaining advantage on every attack you make against your enemy for a full minute instead, which is what you get with Vow of Enmity. This is a single target damage dealing perk for the ages.
In addition to this, you gain access to Hunter's Mark which is a very under rated spell that allows you do deal additional damage every single turn. You also gain access to a few other spells like misty step & haste with great utility. If an enemy attempts to slide by you and attack a more fragile party member, you can follow them after your opportunity attack with relentless avenger at level 7. There is a lot to love with this Oath.
2: Oath of the Crown
Hail to the king, baby! You are a pure, thoroughbred tank. Your party (and king) will love you for keeping them alive.
Between compelled duel being awarded as an additional spell and your Channel Divinity: Champion Challenge, you can aggro enemies like no other subclass in the game. Literally. Nobody else has something close to aggro. If you want to be hailed as a hero this is the subclass for you. In addition to this, you get the amazing spell Spirit Guardians which allows you to dish out tons of damage while you tank groups of enemies.
Divine Allegiance even allows you to take damage for one of your party members instead of them taking damage. Then again, it's only for party members (or creatures) within 5 feet of you so it has limited utility. What do you need more utility for, though? You're the best tank in the game already and you're a phenomenal healer as your base class.
1: Oathbreaker
You have foresaken your vow and been greatly rewarded for your betrayal. Way to incentivize bad behavior.
Oathbreaker is utterly, ridiculously overpowered. So overpowered in fact that most DMs will either wholly outlaw them at the table or require a very good explanation regarding why you have broken your vow in order to let you take this. You immediately have amazing roleplaying potential as an oathbreaker. You took a vow and Sacred Oath to something or someone and planned on ruling your life based upon that, then you completely betrayed it. That did not happen lightly and I'm certain it is a great story.
You get some great spells with this Sacred Oath including Inflict Wounds, Hellish Rebuke, Crown of Madness & Blight among my personal favorites. With Aura of Hate you and any undead or fiendish friends get to add your charisma modifier to every damage roll which is quite a nice addition at level 7, but at level 15 you become resistant to bludgeoning, piercing and slashing damage which is absurd. As your level 20 perk you functionally deal a whole lot of psychic damage to anything that is frightened around you.
The most important ability that you gain comes very early, however, at level 3. With your Channel Divinity Control Undead you get a chance to make any undead that are at least 1 level lower than you in terms of challenge rating your own little companion. You have complete control of this for 24 hours. If you use it every day successfully, you have control in perpetuity. That means at level 3 when you get this, if you encounter a ghast you can make them your own personal little paralysis machine. This gets more ridiculous as you continue to level as well. Imagine having a pet mummy at level 4. Yes, you are likely pure evil. But isn't being evil so much fun?