Nearly everyone I know has different Kay favourites. I loved The Sarantine Mosaic- its probably my second favourite fantasy work after A Song of Ice and Fire, and I reccomend that you read it. However, all of his books, with the exception of The Fionavar Tapestry (which I actually completely hated but which many others like) and A Song For Arbonne (which I found to be too melodramatic and overlong, but overall an all right book) are fantastic; read them all and form your own opinions.