i assume u compare same wattages, lets say 18W vs 18W.. same temperature, either 3000k, 4300k or 6000k.. warmer color might giving u cozy and comfortable at home..

surface is used for no plaster ceiling while downlight need plaster so you would see flat profile with ceiling.. functional wise, both serve same purpose.. unless you compared with eyeball..

in my opinion, if you have plaster ceiling, you could have 3 types of light.. eyeball, downlight and cove light.. all three could serve different purpose..

standard one in market as per what i knew, 18W 6 inch size should be normal one.. dont install too much or else might be too bright.. take note about fan position & shadows angle..