Which mortgage lenders use transunion?

I know for a fact Wells fargo uses Transunion as well as Equifax

Very likely none will use JUST Transunion. When I got my mortgage, they pulled all 3 and took the score from the middle one.

Just about every mortgage lender uses all three major credit reporting agencies which include Equifax. The credit score that is typically used is the middle score, i.e. they "throw out" the highest and the lowest scores from the three reports. If there are two borrowers, the lower middle score of the two borrowers is used.