The phrase "obvious one" means something that is very clear or easy to understand. It refers to something that is so obvious that it doesn't require much thought or explanation. Full definition
Taste is the most obvious difference between olive oil and the store - bought vegetable oils. (mountaintownoliveoil.com)
The building occupants The most obvious difference in cleaning a school as opposed to any other business premises is of course its occupants. (educationbusinessuk.net)
The speaker grill has been shifted from rear to the bottom edge for obvious reasons of sound becoming flat when placed on a table. (phoneradar.com)