Hi folks,
The purpose of this build is to help teamates and absorb damage as much as possible with a fighter. If you are looking for high dpr please check the GWF or the TWF builds. In my opinion, many classes can deal decent damage per round although few classes can mitigate, absorb and protect as well as the fighter.
I suggest two builds, depending on your use (or not) of the feats optional rules. Both are pure fighter builds, they don't take into account multiclassing options.
If you are using feats, I believe the champion archetype is the way to go, whereas if you are not using the feats rules, the battle master is better.
Champion build
Stats priority: STR = CON > DEX > WIS > CHA = INT
A good DEX allows to take a defensive position early in the round and boosts the shield master feat.
Suggested races: Human (for early access to a feat) or Mountain Dwarf.
In the long run both are equal, though maybe the darkvision gives an edge to the dwarf.
Martial Archetype: Champion
Mainly for the two fighting styles and the Survivor bonus. The shield mastery allows to shove every round before attacking thus enhancing the crit probability.
Fighting style: Protection then Defense
If you are playing with melee DPR or healer Protection first, because you need to help your team mates with your reaction.
Feats: Shield master then Sentinel
Shield master first to gain access to a permanent and interesting bonus action every turn.
Skills: Athletics and Perception.
Atheltics is needed for the shove action, Perception prevents surprise.
Background: Any
Weapons: any d8 dmg martial weapon + shield
Round actions:
Bonus action: Second Wind > Shove (before attacking for advantage on prone target)
Action: Attack action
Reaction: Protection > Opportunity attack
Battle master build (no feats)
Stats priority: STR = CON > DEX = CHA > WIS > INT
Good DEX for early defensive position and bonus to parry. Good CHA for rally bonus.
Suggested races: Mountain Dwarf.
No feats allowed.
Martial Archetype: Battle master
Fighting style: Defense
Maneuvers: Rally , Maneuvering Attack , Menacing attack
then Parry, Commander's strike
then Pushing attack, Goading Attack
then Evasive Footwork, Riposte
Skills: Athletics and Perception.
Background: Any
Round actions:
Bonus action: Second Wind (if low hp) > Rally
Action: Menacing or Maneuvering Attack > Commander's strike > Attack action
Reaction: Parry (if low hp)> Opportunity attack > Riposte.
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About AC:
With bounded accuracy, a high Armor Class is the best way to mitigate damage, in my opinion. That's why I suggest the defense fighting style over dueling.
Quick Note on feats:
In my opinion two feats is the maximum if you want to keep good overall stats though you could take three feats with the first build (champion), opening the access to a new build (the twf finesse defender), or gaining more HP, saves or mitigation (with tough, resilient or heavy armor mastery).
Thank you for your comments, ideas, suggestions. 
Kurgag wrote:
Why bother with protection style when taking the sentinel feat? You end up with conflicting reactions, when you could instead combine Duelist+Sentinel to make the reaction attack hurt more.
I agree on Dueling Style over Protection. Going pure turtle seems good, but in play it is often frustrating for the player. A mix of good damage and a feat like Sentinel makes for a dangerous tank that is hard to ignore.
I'd add that Battle Master is, for my money, a much better route for a defender-type fighter. Goading Attack, Distracting Strike, Maneuvering Attack, Sweeping Attack, and Trip Attack are all superb options for a defensive fighter, and can be used in conjunction with Sentinel quite easily.
Heavy Armour Master is also a good feat, at least at lower levels. It would be better if the damage reduction increased at higher level (maybe 5 pts instead of 3 after 10th level), but it would serve quite well til the double digit levels, I think.
I'm a fan of the defensive battle master tank. If you're gonna go human for the feat, I'd start with shield mastery for the abilities it gives -- but heavy armor master is also super great if you want to just be a super turtle. I like goading attack, maneuvering attack, and trip attack as starting maneuvers for battle master.
I see the wisdom in going duelist instead of defensive if you want a little more damage output. Going protection first seems too situational to me because you have to be next to the target -- unless you glue the cleric and wizard to your belt, it's not often you'll get to use the ability (at least with the people I play with). I would go duelist second if I went champion. YMMV!
Jay_Ibero_911 wrote:
I'm a big fan of the shield master feat as well. I had been assuming that "taking the attack option" in order to grant the bonus action would require making a swing as part of the action prior to being able to execute the shove action.
I'm curious to hear the line of reasoning that goes with executing the bonus action prior to making a swing, as that would strengthen the value of the feat.
As you can move between swings when you have multiple attacks, I see no issue with performing the bonus action in between the swings. I'm just not sure how to justify to a DM that by declaring the Attack action I've now triggered the bonus action, even though I haven't actually executed an attack yet.
Technically, by RAW you cannot take the Shove bonus action prior to taking the attack action - as it depends on the attack action in order to be used. With that being said however, I personally see no issue with taking the bonus action first, thereby locking the player into a specific action on their turn.
The only problem that this approach creates, is in the event that an enemy performs a reaction that interrupts your shield action, and invalidates your attack action as a result (such as by crippling you with the incapacitated condition). Such a situation would therefore create a problem wherein you took an illegal bonus action as the attack action was never taken.
Kalani wrote:
Good summary Kurgag, I believe I would allow the bonus action shove to occur eight before the first swing based on that summary.