Hello,
I'll start playing Princes of the Appocalypse (starting Lvl2) next saturnday, so I was thinking about what I should play.
I'm tired of playing support-types (Bard, Wizard) and heavy-Casters (Cleric, Sorceror); I wanted something more simple and self-sustained, which left me with Barbarian (which I scrapped because I want to play a civilized character), Fighter and Paladin.
Now I'm leaning torwards Human Fighter (most likely Battlemaster), but I had the same doubt for both Paladin and Fighter:
*Human with Polearm Master + Great Weapon Fighting style, or
*Human with Heavy Armor Master + Duelist style, using Sword + Shield
I found this topic, which is great about how to optimize and develop the first option. I also think it have some problems with:
1) Action Ecnomy will be tought, expecially reaction. I don't know how this works as the game evolves (mid-high levels).
Action for attack (as usual);
Bonus action, attack with Polearm Master
Reaction being disputed for Opportunity Attacks and battlemaster manuver (Riposte)
2) Other interesting Manuvers (beyonde Riposte) being Precision Strike, Trip Attack and maybe Pushing Attack. Is that right?
On the other hand, thinking about the second option, I have found no dedicated guid except the overall fighter guide (Art of War), which is quite great actually (kudos for it's creator), but still have doubts:
3) I like the idea of ignoring 3 dmg of pretty much every attack... that seems great for a tank at low levels, but does it keep interesting as the game progress? Because I have seen little love for this feat, even if I liked it very much.
4) Other thing I have read in a lot of places is that Shield Master feat seems nice and use a bonus action. However, while reading it, I got the feeling that to use it you use an action and consumes a bonus action. How does it work, really? Or, better yet, can I do the following routine?
a-> Shove/Shield Bash (Bonus Action) to "trip" the target
b -> Attack (Action)
c -> Action Surge, attack (Action)
5) As a broad-range question, how useful is this tank build? Most likely Battlemaster (poor Champion need more love I guess), with Riposte, Precision Strike and... well I have no idea of the last option.
6) These builds could be made with a Paladin instead of a Fighter... but then again... how effective could that be? Not even sure what kind of Paladin I`d like to be:
a -> Ancients have a pretty nice aura, and the theme dies tie in with PotA. But that's that.
b -> Vengeance also seems nice... expecially with Sword & Shield build.
c-> Devotion is kind of meh IMO.
7) However Paladins seems to suffer from lack of power supply: too many good options between spells and smites but so few uses per day (erm, long rest)...
Well... thanks in advance for reading and trying to help with my doubts 
!
Ons
1: Fighter's don't get many reactions or bonus actions, but they get extra feats. So basicly you can pick.
2: Those seem fine.
3: It still helps at high level, since many creatures have multi-attack, but it does lose some of it's luster. But then again, your campaign probably won't reach high levels.
4: You can shove first. Though, you MUST take the attack action if you do.
5: Both are good builds.
6: Paladins are more defensive and group oriented, fighters are more offensive and selfish. Either works fine.
7: Paladins are more spikey, fighter's are more sustained. Either works fine.