Charitable deduction: method used to determine value?

We've been cleaning out our closets and donating old items to local goodwill charities, etc.  They don't estimate the value at the donation drop-off, it's up to us to fill that out.  TT asks the method used to determine value.  I've no clue what to select.  I would think Thrift Shop Value but TT provides no guidance nor does the IRS.