Just pitching in in favour of trying Sword and Board.
If we're sticking to what you listed as your choices, and the levels we are looking at, I'd say straight classed.
But it that's based on the following assumptions:
- Spellcasting for your campaign is RAW and you can't cast Spells like Shield with Sword and Board due to lack of an empty hand (2H weapons bypass that problem entirely so work better)
- Swoard and Board saves you a feat that would otherwise have to go into Great Weapon Master, Mage Slayer is excellent together with Aura of Protection. Legendary Resistance to auto pass once only after you fail the roll goes a long way to let you do your job. Early on this stacks great with Bless to just not suffer anything targeting your INT/WIS/CHA saves. It doesn't work directly on Concentration saves, but most crowd control effects break Concentration, so it helps there.
- OPTIONAL: If magical shields and weapons are somewhat comman option, the dynamig between 1H and 2H changes. Between Dueling Fighting style and having a whole extra slot for scaling AC, the damage difference between 2H and a 1H weapon dice diminishes. Longsword + Dueling FS and Greatsword with Defensive Fighting style at 16 STR are 1D8+5 ~9.5 average damage vs 2D6+3 ~10 average damage (not factoring Crits and Weapon Masteries) and 1 AC difference. If you have access to something like a Flametongue variant of either weapon, the relative DPR difference matters less and less and you'll still do significant damage.
Ofc that also means a +3 Shield could theoretically make that 4 AC difference which is massive. While I would never bank on the +3, but having access to a +1 without attunement and a useful side effect down the line is already significant enough to make it worth looking into, even most cursed shields are kind of a net positive as a tanky frontliner from what I remember.
As a Human getting two Origin Feats on a Frontliner gives you Freedom to pick something you want and still grab Tough to scale your high AC, good saves and Legendary Resistance from Mageslayer even higher.
Heavy Armour Master at 8 rounds out STR to 18 and it's harder to give you bad Concentration Rolls.
Warcaster at 12 to have Advantage on those Concentration Saves and open up Multiclass at 13 to get Shield/Absorb Elements now that you can cast them with full hands. Alternatively a good old regular ASI.
If we aren't going OOV or are Multiclassing out after lvl 6, there's some other interesting options. 2 Frontliners with Sentinel and/or 2024 Protection Fighting Style is a fun combo.