Army Camp Boost out of an ordinary 100% Common Artifact Dig, than I would out of an Epic/Poor or any other Dig.
The artifact you get from any dig site, is equally random. However, when doing 100% commons you can roll the dice on getting the A^B more often (since you can dig more dig sites in the same time).
I avoid sacrificing Artifacts that I do not have duplicates of, at some level, at least until I can verify that I am sacrificing garbage
After playing idle for a while, you'll find that you use a limited set of artifacts a lot, and dont really use the others.
So at that point youre better off sacrificing the artifacts you dont use to upgrade the few that you do use.
It also depends a bit on your playstyle. Some people dont mind constantly swapping e.g. A$B, MCB, RCB, CB for every cache they take, while I would rather have 1 better A$B and then not have to bother with swapping them.
Some links that might be useful for readers on what artifacts to use in general:
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https://docs.google.com/document/d/1EHCM-n_4vq_Hv7V1wo9QSTcRP2ba4qRqBh8fOh5PiKk (see chapter Artifacts and Digs, but the entire document is a must-read for any idle player)
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https://www.warzone.com/wiki/Artifacts#List_of_artifact_types (for understanding the abbreviations people use to describe artifacts)