ISO (i.e. 1x left Shift and an extra key) please!
I don't think the nav cluster in a corner is a good idea, because it makes it impossible to press modifiers (Ctrl) with a palm.
You're lucky that there isn't the question of compatibility with existing keycap sets. ^_^ Here's a suggestion many will hate: 1x Backspace (thus more space on the number row). As a Colemak user, I remap Caps Lock to Backspace anyway. Speaking of that, Caps Lock is a good position for Esc as well.
Another thing, after using TypeMatrix 2030 and playing with the ErgoDox and various grid layouts on my AccessIS keypad for a while, I'm intrigued by the idea of two-row bottom row—basically what you're doing with the nav cluster, but with modifiers. It actually does work, provided the two "minirows" have keycaps of very different profiles.
From the options you've posted, I like the 2A with a split spacebar the most. The number row aligned with the QWERTY row is actually awesome (many would probably hate it though, because it'd mess with their muscle memory), it makes touch typing more straightforward (at least that's my experience from symmetrical layouts).