Which version of UNITE database should I choose?

Recently I have been trying to analysis my ITS amplicon sequences data and I found a little bit confusing thing about the Unite database.
On the Unite database they have distributed two different type of fungi unite database in all formats, not only qiime pre-format:

  1. Includes singletons set as RefS (in dynamic files).

  2. Includes global and 97% singletons.

I have read the README documents in Unite but they did not mention why they posted two versions.
I do know what means about singleton , RefS or dynamic files but I can not figure out what it means together ? :joy:
Does anyone familiar with Unite? Which one should I choose normally? :face_with_raised_eyebrow: