HCMC/NHA TRANG (Ho Chi Minh City)

Hello..I will be.moving to Vietnam in november and I am trying to decide between HCMC or NHA TRANG as the place to live .
I dont need to work but would like to help out voluntarily in orphanage or help with english speaking . Protected content have been to both places before and like both......any thoughts on this matter would be appreciated.....gordon