1. Relative clauses with quantifiers
It is preferable to use that (not which) after the following words: all, any(thing), every(thing), few, little, many, much, no(thing), none, some(thing), and after superlatives.
It was everything (that) he had ever wanted.
There were only a few that really interested him.
Is the blue whale the biggest animal that has ever lived?

2. After numbers and words like many, most, neither, and some, we use of before whom and which in non-defining relative clauses.
These immigrants are registering their children, many of whom were born in the U.S.
Mr. Bittner cut down 25 acres of sweet cherry trees, some of which were 30 years old.