Besides your main weapon I consider the shield to be your most important single piece of gear. I can understand the counter-mainstream thinking with the goal of being different since we have costume slots, but not when concerning shields. Owlite could be called and look like a "Piece of vomit stuck to a board", if it has the most important stats that make me enjoy the game more (i.e. not die a cheap death at the hand of gun puppies, burning or being shocked into permanent stunlock) I'd take it. I consider "and it's not the Owlite" not a valid argument.
But alright, if that's your prerogative. I'll start giving useful comments instead:
Plate shield is almost a perfect FSC shield, but it's not as well rounded as your other options. I consider the crest superior to the skellie shield. So pick either a heater shield or blackened crest.
The heater shield has elemental but just frost resistance, shock is more dangerous since when frozen one enemy hit will set you free again with temporary invulnerability, shock persists for a long time even with the veil. The missing fire resist also hurts in FSC.
The crest of almire is like owlite's stats, just with shadow instead of elemental. Just take care to avoid shielding retrodes, lumbers, gun puppies (most constructs really), charged quicksilver and kats/gremlin projectiles. If you pick something without elemental defense, you should keep the pulsar on you at all times and take it to polaris quickly. Most enemies with elemental damage hit hard but are slow, the pulsar takes advantage of that. Kats are an exception, be careful if they start spamming elemental bullets en masse.
Considering looks, the heater shield is a step back since it looks like a Great defender, the shield you upgraded your mighty defender from but with a color change. Crest of almire looks like an aegis, but with a red tint to it. It's an immediate status symbol too, since you've successfully ran vanaduke 9-10 times.
Since you're one step away from a heater already, get it and use it to run FSC. The lack of fire resist will hurt, but the elemental resist is helpful. You'll have to compensate with skill and maybe polaris shooting. Then save up for a crest and switch in FSC if so inclined for more farming, and also in fiend heavy strata.
Just a small FYI: the divine veil takes a beating from its missing normal defense. Almost everything in the game does 100% normal or 50% with 50% special damage (shadow, pierce, elemental). You could use normal defense on your headpiece too. Hope it helps.
If you want to run T3, you'll probably want a shield for each type of damage.
As for Heater Shield vs Owlite Shield, there is a reason Owlite shield is prefered in most case. They both have elemental resist, so as you point, elemental resistance is good on a shield. The main difference is the status effect resistance. Heater shield as a freeze resistance. While this is annoying, that's a lot less than Fire (you can't shield fire damage) and Shock (which incapacitate you for a second), and Owlite has both of those resistance. That's why you WANT an Owlite shield for most situation. Well, a Heater shield will perform better in an Ice Stratum, but there are more Fire and Shock.
As for a Shadow resistance shield, you basically have two choices : Skelly or Blackened Crest. The real question is : are you able to run FSC enough to have the Blackened ? As for Owlite vs Heater, the Blackened seem to be the better solution because of status effect resistance, but is harder to obtain.
For the Plate Shield, I also heard a lot of good things, but I'll let someone more experienced answer you.
As for the last type of resistance, piercing, only beast and slimes do piercing damage, and they are not the worst enemy to face, so I think, for the moment, you can forget about it.