Watching Blu-ray Discs on 720p HDTVs

[6thDeadlyVenom]

how come for some players and tvs the image looks better when its set at 1080 and converted automatically down while for others it looks better when in the blue ray player menu it's set at 720p like the television accepts? How do you choose or how do you know when the player up/down converts vs the television and how do you generally tell which is better?