It is good for us to be here

Then answered Peter, and said unto Jesus, Lord, it is good for us to be here: (Matthew 17:4)

Three reasons Peter could say "It is good for us to be here."

1/ It was the place where Jesus had brought them to (Matthew 17:1) where he had led them (Mark 9:2) Brought them for the purpose of prayer (Luke 9:28)
2/ It was a place where Jesus was with them .
3/ It was a place of teaching and revelation .