In my case, looking at fighter with +4 dex. Right now he's sporting a +2 agile breastplate at 5th level, for +9 armor and +4 dex for 4550gp. But he wants better than this, eventually.
Looking down the list, perhaps mithral hellknight plate is best, at +2, it increases my armor by 3 to +12, and keeps the +4 dex. But dayum the cost, 15000gp. For 12000 I can just bring my breastplate up to +4 and only be 1 less, and keep the agile part (both armors get -2 armor check penalty.) Then again, at higher levels I could drop another 12000 on the hellknight plate and get it up to +4, but I don't really have that option for the breastplate, I could only spend another 9000gp on it to get +5.
Am I missing something?
And in general, what are the best armor choices for AC focused builds given dex bonus desired? I'm TWF (sword and board) so 16 dex base and +2 belt.
A non-archetyped fighter gets armor training, and so adds to the allowed DEX as he goes up in level. So, at 11th level you can wear any armor you want, made of any material (except maybe gold...) and get your +4 DEX modifier in. So, Full Plate will be worth 9 and 4 more for DEX. This saves you 9000 gold pieces from the mithril version, which may allow for another enhancement.
If you need it sooner, than mithril might be the way to go. If you plan on raising your DEX more than +2 more.
Mithril chain shirt allows +6 DEX modifier, and armor training.
Mithril Breastplate, agile or not, allows +5 DEX modifier.
Steel Full Plate allows +1 DEX modifier.
Celestial Armor gets you to a +8 DEX modifier, on top of armor training.
So, really, it depends on where your dexterity is going to go.
thanks! that's what I was missing, haven't played a straight fighter yet and forgot about armor training.