  We compare several methods for computing disconnected fermion loops
contributing to nucleon three-point functions. The comparison is carried out
using one ensemble of $N_f=2+1+1$ twisted mass fermions with pion mass of 373
MeV. The complete set of operators up to one-derivative are examined by
developing optimized code for mutli-GPUs. Simple guidelines are given as to the
preferable method for each class of operators.
