[MENTION=6804713]lkwpeter[/MENTION], paladins unfortunately don't get the Two-Weapon Fighting fighting style. Both of your hands occupied with weapons would be comparable to a two handed weapon. Without a feat, it's 2x (d6+ability) + d6, 3d6+2x ability if all hit, vs. greatsword of 2x (2d6+ability) for 4d6 + 2x ability if all hit - TWF is inferior except if you are looking at dumping Divine Smites faster at the cost of damage and using your bonus action. That changes at 11th with Improved Divine Smite comes online, but it has the additional drawback of needing more magical weapons.
With spending a feat, Polearm Mastery beats Dual Wielder pretty seriously in terms of damage, though Dual Wielder does have the +1 AC.
But onto the meat of what you were talking about, Spear & Shield + Polearm mastery. There's a slight damage loss vs. a d8 weapon + Shield, averaging 1 point per hit or about 1.3 HP per round with extra attack and a 65% chance to hit. Not a big deal.
Without reach and without a way to disengage, I wouldn't assume to be able to force more than one extra reaction attack an encounter. That will offset the slight damage loss during normal attacks. Sometimes it will end up more, that's just gravy.
So you end up if you use your bonus actoin with three attacks (d6, d6, d4), all adding your STR. With a +4 STR that's about the same damage as two attacks with a d12 weapon with the added benefit of +2 AC and more chances for crits (which do double your Divine Smite dice). (+3 STR your damage is slightly less, but the +2 AC more than makes up for it in a dangerous game.) At 11th with Improved Divine Smite it gets even better.
Dueling will help your damage, Protection will add to your AC. Dueling is quite nice with the extra attack, boosting it above greatsword damage. On the other hand having a +3 total to AC is quite nice as well. I'd make that call based on the others in the party - if several focus around damage and they need a protector, got Protection. If they are more around buffs, debuffs, CC, healing and the like, go for the extra damage. I lean towards the damage - +2 AC from shield plus heavy armor ends up being good enough that an extra +1 is just nice, not spectacular
You do get the fun place where foes may not want to attack you with your high AC, but can't get past / away from you without triggering an OA.
Bonuses to STR will both add directly to damage, but also have a slight multiplicative effect as it also increases you chance to hit.
With shield, you CON drops a little in importance. It's still important for a front liner and for keeping your concentration spells, but say 6/10 instead of 7/10.
You CHR will be useful for your auras at 6th and your fear saves with Conquest / Fallen Aasimar combined with your aura at 7th. So that's useful but can be taken later.
I'd probably say out of your first three ASI/feats, I'd suggest spending at least two on ability scores.
Now, I want to take you in a tangential direction just to consider - back to reach specifically without polearm mastery (or not until way later). This isn't "better", this is just a different focus - you pick what you want. Also, it doesn't come online until 7th so depending on the level range you expect that may just be too late.
At 7th you get your Aura of Conquest, which can reduce Feared opponents to speed 0. You have a few ways to feat opponents, including your Fallen Aasimar ability. The most repeatable one is the Wrathful Smite 1st level paladin spell. Which is a bonus action to cast so it gets in the way of a Polearm Mastery bonus attack.
A frightened foe can still attack you (with disadvantage). Having reach means that unless they have reach they can't get to you in melee and you can just pound on them from safety. Perhaps while standing in a place that blocks others from getting to the rest of your party.
This can still work without reach with a Shield - they would get to attack, but disadvantage combined with a high AC makes it rare for them to hit. Though they still crit at the same rate.
