There is no one way to answer that question. Its a matter of bias. If you like the Air Force then the Air Force is your best choice, If you like the Navy then the Navy is your best choice.
CYA in the Navy, like most places, stands for "Cover Your A$$.
probably marine force recon or scout snipers
The U.S. Air Force has numerous bases outside of the United States.
No
It isn't. The Royal Air Force is an idependent force like the Royal Navy and the Army. The navy and army have their own individual air arms, the Fleet Air Arm and the Army Air Corps but each has individual roles.
The Royal Air Force is England's Air Force. It is part of the Royal military just like the Royal Navy.
some people like to stand around and watch plants grow.
Navy, as it regards a military unit, is not an acronym. I'm sure people have made things up, like Never Again Volunteer Yourself but there is nothing official.
As the Navy and Air Force are both branches of the army, they are both equally hard to get into. Also it depends what you like, whether you would like to sail the world with your crew on a Navy Ship, or would you like to repair planes, pilot planes or refuel planes. They are both equally hard to get into, they both require qualifications if you wish to climb the ranks. However Special Ops teams are the hardest to get into but obviously you must already be in a Military Branch if you wish to join a Spec Ops team most likely they will ask you to join if your skills are Sufficient enough for them or your Commanding Officer will recommend you joining them if you "Stand out from the crowd"
they help us by protecting us by air. just like the navy, army, air force, marines, etc.
It depends on what you like to do. It is focused on clerical work, typing and similar tasks. They maintain the records on all the personnel. It can provide good training in the use of computer systems to do record keeping. And the bonus is that yeoman seldom stand a watch when underway.