Cavalier has caught up with Psi.
Which puts Cavalier + PDK well ahead.
So here's my attempt to combine and simplify it a bit.
Purple Dragon Cavalier
Level 3
Guardian
While a creature is within 5 feet of you, it has disadvantage on any attack roll that doesn't target you.
Rallying Cry
As a bonus action, you can expend a use of your second wind to choose a number of creatures up to your Charisma modifier (minimum 1) who are within 60 feet of you. They gain temporary hit points equal to your fighter level. These last until the creature loses sight of you.
First Aid
As a bonus action, you can expend a use of your second wind to give an creature within reach hit points equal to twice your fighter level. If they are prone, you also help them stand up.
Level 7
Bonus Proficiency
You gain proficiency in Performance, Intimidation, or Persuasion. You gained expertise in on of those skills.
Warding Maneuver
If a creature within 5' of you takes damage, you can use your reaction to give that creature resistance to that damage.
Level 10
Inspiring Surge
As a reaction on another creatures turn while they are within 60', you may expend your Action Surge to give them a bonus action. That extra action can not be a Magic action.
Hold the Line
Enemies who start their turn within 5' of you have their speed reduce by half until the end of their turn.
Level 15
Bulwark
When you and at least one other creature make a saving throw against the same effect, such as a fireball, you can expend a use of Indomitable to give all the targets of that effect advantage on that saving throw with a bonus equal to your Charisma modifier.
If the effect causes multiple saving throws, this only applies to the first one each creature makes.
Level 18
Vigilant Defender
In combat, you get a special reaction that you can take once on every creature's turn, except your turn. You can use this special reaction only to make an opportunity attack or Warding Maneuver, and you can't use it on the same turn that you take your normal reaction.
Team Work Fighting Style
Level 1 feat.
When you would make a weapon or unarmed attack, you may chose to feint in order to provide an opening for an ally. You do not make an attack roll, instead chose a willing ally. They immediately use their reaction to make a weapon or unarmed attack against your target.