Depends on what you are hunting, where you are hunting, your skill level and your pocket book.
TASCO
The best you can afford.
Best left to a good gunsmith.
Impossible to answer without knowing what your end state is. Even then, "best" depends on your pocket book, skills, rifle, etc..
The best you can afford for your ultimate end use. You fail to mention if you are a hunter, paper puncher, plinker, etc..
Best left to a gunsmith
The m1 garand for its power and it can have a sniper scope
Best left to a gunsmith
One that was designed for air rifles. Best will be determined by your intended use and how much you spend.
"Best" is a subjective term that will be based on your pocketbook and what you are using the rifle for.
Nikon Prostaff is an excellent variable scope for under $250. Excellent optics, can't beat it for the price.
Some scopes can cost more than the Air Rifle. Leapers makes some excellent scopes for around $250. Whatever scope you purchase make sure it is designed for air rifles. Air rifles, because of their forward / reverse kick, can break a regular hunting scope not designed for this type of rifle.