A few more notes (sorry, I should have reread everything), I was initially going to push AC until I heard there were penalties for medium/heavy armor. The Fighter/Guardian subclass is essentially a sticky fighter that keeps enemies on him so turtling makes sense. I don't know what the penalties are (heat wise), but I decided to sacrifice that for genre. I didn't want to just run a Dex fighter though because I already play a dex based paladin and I wanted new ground to cover.
So, if high AC wasn't an option that means go for high HP since I'll take a lot of hits (since I'm sticky) and push damage. I considered doing a Polearm Master build to really abuse the Guardian mechanics, but if felt cheap so I just went for Great Weapon and max damage. The Flametongue has great damage potential, but fire resistance is common. That's the thought behind a backup weapon. With the flamtongue and GWM, I have three attacks at +4 to hit (+9 -5=+4) for 2d6+15+2d6 fire damage each. That should average around 29 damage per hit (7+15+7) and 87 damage per round. Dropping GWM (if they have high AC), 2d6+5+2d6 (7+5+7) which is still an average of 19 damage per hit and 57 damage per round. I should be dangerous.