HDI is a better index of development because 

HDI (Human development index):

It is a composite statistic of life expectancy, education, and income indices used to rank countries.

For constructing HDI, we have to prepare an index number for each of the three dimensions of human development.

• Long healthy life dimension – life expectancy index
• Knowledge dimension – Education index
• Standard of living dimension – GDP per capita

As it covers income, health, and education aspects of development, it is a better index.

HDI is calculated by taking an average of three-dimension indices.

HDI = (L.E.I. + E.I. + GDP Index)/3