Juan Mascaro's edition of the Gita is undoubtedly one of the more attractive versions for the general reader who is approaching the Gita for the first time. Mascaro, besides being a Sanskrit scholar, is a sensitive translator who clearly resonates to the Gita. He tells us that the aim of his translation is "to give, without notes or commentary, the spiritual message of the Bhagavad Gita in pure English." To suggest just how well he has succeeded, here is his rendering of Verse II.66:
"There is no wisdom for a man without harmony, and without harmony there is no contemplation. Without contemplation there cannot be peace, and without peace can there be joy?"
Many readers will probably be content to remain with Mascaro, and it certainly seems to me that his translation reads beautifully and that a fair number of his verses have never been bettered by others. But the Gita is not quite so simple as it may sometimes appear. If we want to arrive at a fuller idea of just what the Gita means by "wisdom," "harmony," "contemplation," "peace," and so on, we will need to consult other and fuller editions.
There are many editions which, besides giving a translation of the Gita, also give a full commentary such as the excellent one by Sri Aurobindo in his 'Bhagavad Gita and Its Message' (1995). Others, besides giving a commentary and notes, also give the Sanskrit text along with a word-by-word translation. Some of these even include the commentary of the great Indian philosopher, Shankara (c. + 788 to 820), such as the very fine edition by Swami Gambhirananda (Calcutta: Advaita Ashrama, 1995, which may be available through the Vedanta Press, CA). Here is the latter's English rendering of Verse II.66:
"For the unsteady there is no wisdom, and there is no meditation for the unsteady man. And for an unmeditative man there is no peace. How can there be happiness for one without peace?"
This may not seem to have carried us much beyond Mascaro until we start looking at Shankara's commentary, of which the following provides a taste:
"Ayuktasya, for the unsteady, for one who does not have a concentrated mind; na asti, there is no, i.e. there does not arise; buddhih, wisdom, with regard to the nature of the Self; ca, and; there is no bhavana, meditation, earnest longing for the knowledge of the Self; ayuktasya, for an unsteady man. And similarly, abhavayatah, for an unmeditative man, who does not ardently desire the knowledge of the Self; there is no shantih, peace, restraint of the senses. Kutah, how can there be; sukham, happiness; ashantasya, for one without peace? That indeed is happiness which consists in the freedom of the senses from the thirst for enjoyment of objects; not the thirst for objects - that is misery to be sure. The implication is that, so long as thirst persists, there is no possibility of even an iota of happiness!" (page 112-3).
For anyone who would like to see a full treatment of the language of the Sanskrit text, there is Winthrop Sargeant's stupendous labor of love, 'The Bhagavad Gita' (SUNY, 1984) which offers a complete grammatical description of every single Sanskrit word in the text, along with much else.
Finally, for anyone who would like to look at a first-rate study of the Gita, there is Trevor Leggett's 'Realization of the Supreme Self - The Yoga-s of the Bhagavad Gita' (Kegan Paul International, 1995). This is a superb work with an intensely practical bent which sees the Gita, not so much as a metaphysical treatise but as a book of practical instruction. I used to think I knew the Gita before I discovered Leggett!
But despite the great wealth of available editions, of which I've mentioned only a few here, I still find myself returning to Mascaro from time to time. A perfect translation of the Gita into English is probably unattainable, but Mascaro seems to have come as close as anyone is ever likely to do. His version has a tendency to send down roots and grow in the mind.