You need at least 490 Def to be uncritable, which is more important than uncrushable.
After that, you'll work on getting uncrushable.
You need 7.9 Block Rating for 1% more uncrushable. This doesn't give avoidance.
You need 15 Defense Rating for 1% more uncrushable. This gives 0.75% avoidance.
You need 18.9 Dodge Rating for 1% more uncrushable. This gives 1% avoidance.
You need 20 Defense Rating for 1% avoidance. This gives 1.33% more uncrushable.
You need 22.4 Parry Rating for 1% more uncrushable uncrushable/avoidance.
You need 25 Agility for 1% more uncrushable/avoidance.
As you see, Defense and Dodge are about as useful for getting uncrushable as one gives more, but the other gives more avoidance. Parry and Agility are worse of in both aspects. Block will help if it's hard to read, but since it doesn't do anything besides granting uncrushability, it's a stat not sought after later on.
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Zoe's guide to building your tankadin