This may be a dumb question, but what makes more sense for exhoing strike builds. I know they use both damage types, so which colossal stone would give the most benefits?

Echoing strike uses physical damage, so physical one

Echoing strike almost entirely physical dmg. That said, you will not get the ED% bonus from the jewel unless you use it in a weapon.

Source:

https://forums.d2jsp.org/topic.php?t=74198145

The ed / min / max dmg bug has been a thing for years. Oversight from the new devs / llama