Terms for uncountable nouns: quantity versus amount

Hi Teachers,
To explain sentence 'a' it is appropriate to use sentence 'b', if I'm not mistaken.
a) There are a lot of books on the shelf.
b) There is a big number of books on the shelf.
Which one is most appropriate to explain sentence 'a', 'b' or 'c'?
a) There is a lot of traffic in the street.
b) There is a big quantity of traffic in the street.
c) There is a big amount of traffic on the street.
The issue is, which term is better for uncountable nouns, 'quantity' or 'amount'?
Thanks in advance