What is the most efficient way to compare 2 customer's addresses from a Customer record in a SS2.0 User Event script?

if you mean code efficiency, with NFT I'd just use

_.isEqual(addr1, addr2)

for equality.

I meant more along the lines of loading each customers Address subrecord and comparing

in that case (if using NFT) you can use any answer you find on the internet (e.g. stack overflow) since the objects you're comparing are plain JS objects