Ok so ramping up my first big 5e campaign. Low level now, with hopes of running this character to high level.

Our group seems to have a lot of damage output and mobility, but no one could really take a sustained beating (Warlock, monk, rouge, great axe Barbarian). So I created and Oath of Ancient Paladin to stand toe to toe with Monsters while the party pokes holes in them. Now having to pick fighting style i'm at a crossroads. First thought was build tanky and stick with shield and warhammer if the party needs protction, But Ill eventually get plate anyways and I like playing different things and ive never used a polearm before and no one else in our party seems interested in using one either. Ive have done some reading and it looks like the whole (glaive, PAM, Sentinel combo) could be an awesome approach to being a tar pit in the battle field allowing my guys to move freely.

I currently have level 2.   17st 8Dex 14con 8Int 10wis 16cha.   My two trains of thought....

1. Since im not worried about dmg output: Take defense fighting style (passing on GWF) and get +1 Ac then when i get a polearm i can ditch the shield and only lose 1 AC total.  have battlefield control at minimal AC loss.

2. I've heard that AC is hard to come by in 5e and I should stick with shield and take defensive style for ultimate AC build. (curious about how much AC plays into higher level D&D battles, or if it gets more about saving throws and magic.)

I put my highest importance on team cohesion and party dynamics rather then my individual performance. Just wanted to see what the D&D internet thought we would be more effective way of protecting my team (my Biggest goal)

Plate mail ac 18
Shield +2 AC
Fighting style- defense +1 AC
level 1 spell shield of faith +2 AC concentration
23 AC w/o any magical items, always go charging into combat, because you are not super smart (int 8) and force as many attacks of opportunity as you can. 
Have your warlock take the 10 push eldritch blast invocation for more synergy.

I would consider oath of conquest for armor of agathys and eventual fear dropping move speed to 0 bubble around yourself to hold them on you, wasting most attacks on your ac 21 or 23 depending on if shield of faith is up, and taking damage from agathys if they do hit you automatically

Quote from Sillvva>>

Polearm Master + Sentinel is a great way to protect your back line.

The only issue with this is that unless you're a variant human, you're giving up two ASI, and I'd argue Polearm Master doesn't add much to your crowd control abilities. (Sure, it stops enemies from reaching you, but you only get 1 reaction, so if multiple enemies are involved it doesn't make sense to waste it on an enemy that was going to engage you anyways.) On the other hand, increasing your Strength helps your opportunity attacks hit, and if you opt for a shield then Shield Master lets you limit an enemy's movement by knocking them prone.

However, lots of defense, and no offense means a smart enemy would just ignore you.

This. And as you level up, a smart enemy might still choose to provoke an opportunity attack, because there's only so much damage you can do in a single attack.

When push comes to shove, I'd recommend Dueling or Protection Fighting Style over Defense. +1 AC is good, but killing the monster sooner or saving a weaker party member from a hard-hitting attack is usually better - and as a Paladin, your auras create an incentive for party members to stay close to you.

Your best choice for protecting your party is with battlefield control. Spells like Compelled Duel will also help.