For example, the La Niña in 1988 was stronger than the La Niñas in 1995 and 1998, and the 1997-1998 and 2015-2016 El Niños are unusually strong compared to those in 1991-1992, 1993, 1994 and 2010.
Notice that El Niño and La Niña events vary considerably in strength. For example, the La Niña in 1988 was stronger than the La Niñas in 1995 and 1998, and the 1997-1998 and 2015-2016 El Niños are unusually strong compared to those in 1991-1992, 1993, 1994 and 2010.  Here is a list of list of El Niño and La Niña events (by year) from NOAA ESRL PSD, and another list of El Niño and La Niña years (by month)  provided by the National Center for Environmental Prediction (NCEP).