Jami' At-Tirmidhi (6 Vol. Set)
Al-Hafiz Abu Al-Fall Al-Maqdisi said: "I heard Al-Imam Abu Ismail `Abdullah bin Muhammad Al-Ansari in Harrah " when Abu `Eisa At-Tirmidhi and his book was mentioned before him " saying: `To me, his book is better than the book of Al-Bukhari and that of Muslim. Because only one who is an expert in knowledge can arrive at the benefit of the books of Al-Bukhari and Muslim, whereas in the case of the book of Abu `Eisa, every one of the people can reach its benefit."
In Jami`Al-Usul, Ibn Al-Athir said: "(It) is the best of the books, having the most benefit, the best organization, with the least repetition. It contains what others do not contain; like mention of the different Madhhabs (views), angles of argument, and clarifying the circumstances of the Hadith being authentic, weak, Gharib (odd), as well as disparaging and endorsing remarks (regarding narrators)."
Similarly, more was said by Ibn Al-`Arabi in Aridah Al-Ahwadhi who listed fourteen categories of benefit in the book.
Adh-Dhahabi said: "In Al-Jami' there is useful knowledge, abundant benefits, and a summary of the issues. It is one of the Usul of Islam, if not for the tarnish of the inauthentic Ahadith in it, some of which are fabricated " and most of that are about virtues." Buy this Book