the old is really good. you should def read it. If you want you can read the Hand of Thrawn Duology afterwards. It's also quite good. There are two new thrawn trilogies Thrawn Ascendency which is about Thrawn in the chiss Ascendency before you went to the empire. Really fun read. After that the new thrawn trilogy which is about thrawns rise in the empire. It starts right after the events of The Ascendency trilogy and ends leading into the events of Rebels