Abstract: A generalized advantage factor, F= G·Ri/R, is proposed to represent real improvement in detection limits or relative counting statistics achieved by using ENAA. The traditional Brune's and recently suggested Bern's definitions can be considered as its two special cases with G=Ri and G=1 respectively.In order to obtain optimum advantage factor, it is recommended that different channels (or even different reactors) be used for total reactor neutron spectrum activation (TNA) and epithermal neutron activation (ENA).The merits and drawbacks of Cd and BN shielders are reviewed in detail.In addition, advantage factors of 38 reactions are determined with TNA and ENA in different reactors. Interference factors for 33 interference reactions with both ENA and TNA are estimated and interference multiplications caused by ENA are also discussed.