It is difficult to say which is the best translation. I have copied several editions below. Perhaps this will make it easier for you to search on amazon.com for the titles and read different reviews so you can choose one that is most helpful for you.
Gudo Wafu Nishijima and Brad Warner Fundamental Wisdom of the Middle Way: Nagarjuna's Mulamadhyamakakarika Monkfish Book Publishing 2011
ISBN 978-0-9833589-0-9 A modern interpretation from a Zen perspective.
Mabja Jangchub Tsöndrü Ornament of Reason: The Great Commentary to Nagarjuna's Root of the Middle Way Snow Lion 2011 ISBN 978-1-55939-368-3
Commentary translated by The Dharmachakra Translation Committee.
Jones, Richard H. Nagarjuna: Buddhism's Most Important Philosopher Booksurge 2010 ISBN 978-1-4515-3979-0
Translation into idiomatic English with commentary and translations of other works by Nagarjuna.
Padmakara Translation Group The Root Stanzas on the Middle Way Éditions Padmakara 2008 ISBN 978-2-916915-44-9
This volume, containing both the Tibetan text and translation, was made to mark the visit of His Holiness the Dalai Lama to France in August 2008, and as a support for the teachings scheduled for that occasion.
Luetchford, Michael J. Between Heaven and Earth - From Nagarjuna to Dogen Windbell Publications 2002 ISBN 978-0-9523002-5-0
A translation and interpretation with references to the philosophy of Zen Master Dogen.
Batchelor, Stephen Verses from the Center Diane Publishing 2000 ISBN 978-1-57322-876-3 Batchelor's translation is the first nonacademic, idiomatic English version of the text.
McCagney, Nancy Nagarjuna and the Philosophy of Openness Rowman & Littlefield 1997 ISBN 978-0-8476-8626-1 Romanized text, translation and philosophical analysis.
Garfield, Jay L. The Fundamental Wisdom of the Middle Way Oxford University Press 1995 ISBN 978-0-19-509336-0 A translation of the Tibetan version together with commentary.
Kalupahana, David J. Nagarjuna: The Philosophy of the Middle Way State University of New York Press 1986 ISBN 978-81-208-0774-7 Romanized text, translation, and commentary. Interpretation of the text in the light of the Canon.
Inada, Kenneth K. Nagarjuna: A Translation of his Mulamadhyamakakarika With an Introductory Essay The Hokuseido Press 1970 ISBN 978-0-89346-076-1 Romanized text and translation.
Streng, Frederick Emptiness: A Study in Religious Meaning Abdingdon Press 1967 (predates ISBN) Translation and considerable analysis.
Mūlamadhyamakakārikā
It is difficult to say which is the best translation. I have copied several editions below. Perhaps this will make it easier for you to search on amazon.com for the titles and read different reviews so you can choose one that is most helpful for you.
Gudo Wafu Nishijima and Brad Warner Fundamental Wisdom of the Middle Way: Nagarjuna's Mulamadhyamakakarika Monkfish Book Publishing 2011
ISBN 978-0-9833589-0-9 A modern interpretation from a Zen perspective.
Mabja Jangchub Tsöndrü Ornament of Reason: The Great Commentary to Nagarjuna's Root of the Middle Way Snow Lion 2011 ISBN 978-1-55939-368-3
Commentary translated by The Dharmachakra Translation Committee.
Jones, Richard H. Nagarjuna: Buddhism's Most Important Philosopher Booksurge 2010 ISBN 978-1-4515-3979-0
Translation into idiomatic English with commentary and translations of other works by Nagarjuna.
Padmakara Translation Group The Root Stanzas on the Middle Way Éditions Padmakara 2008 ISBN 978-2-916915-44-9
This volume, containing both the Tibetan text and translation, was made to mark the visit of His Holiness the Dalai Lama to France in August 2008, and as a support for the teachings scheduled for that occasion.
Luetchford, Michael J. Between Heaven and Earth - From Nagarjuna to Dogen Windbell Publications 2002 ISBN 978-0-9523002-5-0
A translation and interpretation with references to the philosophy of Zen Master Dogen.
Batchelor, Stephen Verses from the Center Diane Publishing 2000 ISBN 978-1-57322-876-3 Batchelor's translation is the first nonacademic, idiomatic English version of the text.
McCagney, Nancy Nagarjuna and the Philosophy of Openness Rowman & Littlefield 1997 ISBN 978-0-8476-8626-1 Romanized text, translation and philosophical analysis.
Garfield, Jay L. The Fundamental Wisdom of the Middle Way Oxford University Press 1995 ISBN 978-0-19-509336-0 A translation of the Tibetan version together with commentary.
Kalupahana, David J. Nagarjuna: The Philosophy of the Middle Way State University of New York Press 1986 ISBN 978-81-208-0774-7 Romanized text, translation, and commentary. Interpretation of the text in the light of the Canon.
Inada, Kenneth K. Nagarjuna: A Translation of his Mulamadhyamakakarika With an Introductory Essay The Hokuseido Press 1970 ISBN 978-0-89346-076-1 Romanized text and translation.
Streng, Frederick Emptiness: A Study in Religious Meaning Abdingdon Press 1967 (predates ISBN) Translation and considerable analysis.