ometimes it's difficult to know which way is the best way to say something or write it.
Here is a table to add to. Be aware that this can only be a guideline.
Some words are perfectly acceptable when used with another meaning, others may be acceptable in slightly more, or slightly less formal contexts.

Formal / informal

many, quite a few, a number of
a lot of
very good, quite good
really good
I disapprove
I don't agree
.a great deal of