That depends on your target build. Assume you value protect and foundation to 9 each, and you have a pass block custom. Also assume the opportunity cost for blocking is 4:1, as I'm assuming you took blocking to 68 and stopped there. Who cares what natural gains took you to, the opportunity cost was when you decided to stop spending, so at 4:1.
That's an immediate 12 SP the first gets you.
The SA tree will look like
x-x-8-x-8.
With AE, you'll only need the 8 to be a 4.
Protect: 2-4-8-2-4
Foundation: 1-2-4-4-8
value difference: protect piece costs... (1 extra, 4 extra, 14 extra, 4 less, 18 less) = 3 less.
So the foundation piece saved you 9 SP in achieving your goal of 9 protect, 9 foundation, and 3 more points in blocking. The protect piece did bring you extra pass block, shock block, and less absorb pain in prereqs. I'd value absorb pain at nothing, but it did net you 5 SPs saved in pass block and shock block, which are arguably good pieces.
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Math'D. If you want protect and foundation high, and that blocking means something to you, the foundation piece is better.
If you're satisfied leaving foundation lower, the protect piece holds far more value.
If you have a good build, I'd take the first. You'll have enough SPs down the line to get protect up anyways, but that 3 blocking is something that really becomes intangible down the road, as you are unable to revisit blocking due to its high cost.
Not to mention, you can always keep shopping and find another protect piece, I get them once a week or so for my OT (if not more, every 4-5 days?). Gobble up the +3+SA while you can, and build both up