Either, Any
Incorrect : Any of these two books is good.
Correct : Either of these two books is good.
Incorrect : Either of these three pens will do.
Correct : Any of these three pens will do.
Note: "Either' means one or the other of two persons or things. And "any" means one of three or more persons or things. So "any" should not be used when two persons or things are involved and "either' should not be used when more than two persons or things are involved. The negative of “any' is “none" and that of "either" is “neither".
For example:
Neither of the two books is good.
None of these three books is good.
