When installing GFCI outlet receptacle on a 20 amp breaker, what should be used, a 20 amp GFCI, or is a 15 amp GFCI OK too?
The rules that apply to installation of a GFCI outlet receptacle on a 15 or / and 20 amp rated circuit breaker are the same as the ones that apply to a regular outlet receptacle. Additionally, there may be some regulations applicable only to a particular area this GFCI is going to be installed, or your local jurisdiction requirements.