Q.Hi Which type is the best,..
Horizantal or vertical...for family of 4 members in apartment of 4th floor...we have enough space to fit both type
500
Kindly prefer this link for Long answer
https://aosmithindia.com/assistance/faqs/water-heater
Go with vertical but don’t take AO SMITH. You will repent down the line as they have no after sales support. They will stop caring after their product is sold. Sharing this experience after having two AO SMITH water heaters in my home