The Best of James H. Schmitz was published in 1991 by NESFA and is described in the NESFA Press on-line catalog . Also, the Linkoping Sci-Fi archives contain a review of the book.
Stories in The Best of James H. Schmitz :
Mischief in the Spaceways (intro by Janet Kagan)
The Second Night of Summer
Sour Note on Palayata
Bibliography (from the Whole Science Fiction Database
Illustrations by Merle Insinga