I’m struggling a bit with how to build a Cavalier; especially feat and weapon choices. Like trying to reconcile the fact that you are going to get attacked a lot, so you want a shield; but you also want reach to maximize the effectiveness of hold the line; and the L18 ability seems like a natural fit for a polearm master, but then you’re dropping a ton of AC by mot wearing a shield in Tier 4 (when you may very well have a +2 or +3 shield).
Whip is one-handed and provides reach, but that seems like a super weird solution. And lance is one-handed with reach while mounted, but becomes super awkward if you dismount or if you’re trying to stay within 5’ of your target.
Any advice?
Personally I think you should own what the archetype enables instead of worrying about AC, and that my friend is slaughter the enemy and with the pole arm move away after attacks due to reach with your 40-50 ft of movement on horse.
I would do it like this, my example will be a level 6 cavalier (either a half orc or half elf (more on half elf later)). Your 2 feats are mounted combatant (Advantage against a lot of creatures and protection for your ride) and polearm master.
-Now Half orc as race is simple, you have advantage from mounted combatant so good chance to use savage attack on your normal attacks and opportunity attack when enemy enters polearm reach; also once a day avoid being knocked out. I would probably go for this race over others.
-As for Half-elf, maintain the strength build and at level 8 take elven accuracy so now while using mounted combatant you pretty much have constant advantage against most creatures. A bit of work but good dps potential.
Now for your defence concerns
- With your polearm use hit and run tactics, make them chase you and they will likely struggle while you are mounted. Can't hit you if they can't reach you.
-Can't hit you if they are dead, make sure to hit them hard and fast
- Take the fighting style that increases AC by 1, with plate you will have 19 AC
-If defence is of utmost importance use the dodge action, it will still be possible for you to attack with your polearm reaction
-Ultimately defend yourself with strategy not stats, a good party will adapt to the parties strengths and find ways to cover weaknesses.