Between largest and biggest, that is not considering possible other alternatives, one can say that
- largest is formal
- biggest is informal
One does not generally use biggest in formal mathematical text or for that matter, in any formal English text for the most part.
Then I found,
Rachel Wicaksono on BBC's Learning English
quantity words …
'large', more often than 'big', is used with the following quantity words:
'a large amount', 'on a large scale', 'a large number of', 'a large quantity of', 'a large proportion', 'to a large extent', 'a large percentage of', 'a large part of', 'a large volume' and 'a large area'
- Big vs Large vs Great
- Difference Between Big and Large