SELECT   max(reit),     
FROM Book b,  Author2Book a
WHERE b.id  = a.book_id      -- или по одному AND author_id = 24
GROUP BY author_id              -- по всем авторам

select max( a.reit) as best, a2.name
from   Books a
JOIN Author2Books an2 ON ( a.id = an2.books_id )
JOIN Authors a2 ON ( a2.id = an2.author_id )

where  a.reit = ( select max(reit) from Books b, Author2Books an
      where  b.id = an.author_id  and a.id = b.id  group by an.author_id )
GROUP BY a2.name