Best use of 8th stone?

[Echo]

Working towards this and was wondering if there's a standard thing to pick? Maybe

I've been playing a void arrow focused huntress. Originally as elemental, but found much more success just focusing on raw damage and shadow imbues.

The crit/ancestral chance generic looks good as general pick. Otherwise grabbing lightning imbue to avoid lots of crappy nodes in a crackling thunder bow build also seems promising.